Definition of "key"

key¹

/kiː/

noun
plural keys
1. An object designed to open and close a lock.
  Quotations
  We tiptoed into the house, up the stairs and along the hall into the room where the Professor had been spending so much of his time. 'Twas locked, of course, but the Deacon man got a big bunch of keys out of his pocket and commenced to putter with the lock.
  1913, Joseph C. Lincoln, chapter 13, in Mr. Pratt's Patients
2. An object designed to fit between two other objects (such as a shaft and a wheel) in a mechanism and maintain their relative orientation.
3. A crucial step or requirement.
  Quotations
  Those who are accustomed to reason have got the true key of books.
  a. 1705, John Locke, “Of the Conduct of the Understanding”, in Posthumous Works of Mr. John Locke: […], London: […] A[wnsham] and J[ohn] Churchill, […], published 1706
  who keeps the keys of all the creeds
  1850, [Alfred, Lord Tennyson], In Memoriam, London: Edward Moxon, […], (please specify |part=prologue or epilogue, or |canto=I to CXXIX)
4. A guide explaining the symbols or terminology of a map or chart; a legend.
5. A guide to the correct answers of a worksheet or test.
6. (computing) One of several small, usually square buttons on a typewriter or computer keyboard, mostly corresponding to text characters.
7. (music)
  1. In musical instruments, one of the valve levers used to select notes, such as a lever opening a hole on a woodwind.
  2. In instruments with a keyboard such as an organ or piano, one of the levers, or especially the exposed front end of it, which are depressed to cause a particular sound or note to be produced.
8. (music) A scale or group of pitches constituting the basis of a musical composition.
  Quotations
  A girl, it is true, has always lived in a glass house among reproving relatives, whose word was law; she has been bred up to sacrifice her judgments and take the key submissively from dear papa; and it is wonderful how swiftly she can change her tune into the husband's.
  1881, R.L. Stevenson, Virginibus Puerisque
  1. The lowest note of a scale; keynote.
  2. In musical theory, the total melodic and harmonic relations, which exist between the tones of an ideal scale, major or minor; tonality.
  3. In musical theory and notation, the tonality centering in a given tone, or the several tones taken collectively, of a given scale, major or minor.
  4. In musical notation, a sign at the head of a staff indicating the musical key.
9. (figurative) The general pitch or tone of a sentence or utterance.
  Quotations
  2. Queen. […] Deere Glasse of LadiesBid him that we whom flaming war doth scortch,Vnder the shaddow of his Sword, may coole us:Require him he advance it ore our heades;Speak't in a womans key: like such a womanAs any of us three; weepe ere you faile; lend us a knee;But touch the ground for us no longer timeThen a Doves motion, when the head's pluckt off:Tell him if he i'th blood cizd field, lay swolneShowing the Sun his Teeth; grinning at the MooneWhat you would doe.
  1613–1614 (date written), John Fletcher, William Shak[e]speare, The Two Noble Kinsmen: […], London: […] Tho[mas] Cotes, for Iohn Waterson; […], published 1634, Act I, scene i, page 1
  You fall at once into a lower key.
  ?, William Cowper, Conversation
10. (advertising) A modification of an advertisement so as to target a particular group or demographic.
  Quotations
  Another popular way to key ads and mailings is to use a suite number, room number, department number, desk number, etc. as part of the ordering address. With a classified ad, using such a key may increase your ad cost.
  1998, Mail Order Success Secrets
11. (botany) An indehiscent, one-seeded fruit furnished with a wing, such as the fruit of the ash and maple; a samara.
12. (historical) A manual electrical switching device primarily used for the transmission of Morse code.
13. (cryptography) A piece of information (e.g., a password or passphrase) used to encode or decode a message or messages.
14. (Internet) A password restricting access to an IRC channel.
  Quotations
  if you know someone who is in the channel, you can query them and ask for the key.
  2000, Robert Erdec, “Re: Help; mIRC32; unable to resolve server arnes.si”, in alt.irc.mirc (Usenet)
15. (databases) In a relational database, a field used as an index into another table (not necessarily unique).
16. (computing) A value that uniquely identifies an entry in a container.
17. (basketball) The free-throw lane together with the circle surrounding the free-throw line, the free-throw lane having formerly been narrower, giving the area the shape of a skeleton key hole.
18. (biology) A series of logically organized groups of discriminating information which aims to allow the user to correctly identify a taxon.
19. (architecture) A piece of wood used as a wedge.
20. (architecture) The last board of a floor when laid down.
21. (masonry) A keystone.
22. That part of the plastering which is forced through between the laths and holds the rest in place.
23. (rail transport) A wooden support for a rail on the bullhead rail system.
24. The degree of roughness, or retention ability of a surface to have applied a liquid such as paint, or glue.
25. (cartomancy) The thirty-third card of the Lenormand deck.
26. (print and film) The black ink layer, especially in relation to the three color layers of cyan, magenta, and yellow. See also CMYK.
27. (computer graphics, television) A color to be masked or made transparent.
  Quotations
  You can easily create this type of user interface by creating a bitmap with certain portions set to a predefined color you want to use as the transparency key.
  2004, Mark Schmidt, Simon Robinson, Microsoft Visual C# .NET 2003 Developer's Cookbook, page 195
  There are key controls that adjust the “slice level” or the level at which the key kicks-in and starts cutting a hole for the “fill” […] Chroma key is another form of keying, which derives the key cutter or hole from a selected color.
  2016, Jerry C. Whitaker, The SBE Broadcast Engineering Handbook
adjective
comparative more key, superlative most key
1. Indispensable, supremely important.
  Quotations
  Lukas intimates that one of Disney's key attractions was "Main Street USA,” which "mimicked a downtown business district just as Southdale" had done.
  2007, Mark H. Moss, Shopping as an Entertainment Experience, page 46
  The question of the plausibility of the counter-factual is seen as key in all three discussions of allohistorical fiction (as it is in Demandt's and Ferguson's examinations of allohistory) (cf. Rodiek 25–26; Ritter 15–16; Helbig 32).
  2014 October 14, David Malcolm, “The Great War Re-Remembered: Allohistory and Allohistorical Fiction”, in Martin Löschnigg, Marzena Sokolowska-Paryz, editors, The Great War in Post-Memory Literature and Film‎, Walter de Gruyter GmbH & Co KG., page 173
  The enemy is moving troops through a key area. Distrupt their activities to open some holes in their defenses.
  2017, BioWare, Mass Effect: Andromeda (Science Fiction), Redwood City: Electronic Arts, PC, scene: Disrupt Enemy Movements
2. Important, salient.
  Quotations
  Throughout the 1500s, the populace roiled over a constellation of grievances of which the forest emerged as a key focal point. The popular late Middle Ages fictional character Robin Hood, dressed in green to symbolize the forest, dodged fines for forest offenses and stole from the rich to give to the poor. But his appeal was painfully real and embodied the struggle over wood.
  2006, Edwin Black, chapter 2, in Internal Combustion‎
  With the north London derby to come at the weekend, Spurs boss Harry Redknapp opted to rest many of his key players, although he brought back Aaron Lennon after a month out through injury.
  2011 September 29, Jon Smith, “Tottenham 3 - 1 Shamrock Rovers”, in BBC Sport‎
verb
third-person singular simple present keys, present participle keying, simple past and past participle keyed
1. To fit (a lock) with a key.
2. To fit (pieces of a mechanical assembly) with a key to maintain the orientation between them.
3. To mark or indicate with a symbol indicating membership in a class.
  Quotations
  So I worked on a tissue-paper copy of the perimeter plan, outlining groupings of plants of the same species and keying them with letters for the species.
  1996 January, Garden Dsign Ideas, second printing, Taunton Press, page 25
  The volume closes with thirty pages of "Notes, critical and explanatory," in which Thomson provides seventy-six longer or shorter notes keyed to specific sections of the synopsis.
  2001, Bruce M. Metzger, The Bible in Translation, page 87
  Talk about similarities between the words and write them below to the left of the anchor, keying them with a plus sign (+). Talk about the characteristics that set the words apart and list them below the box to the right, keying them with a tilde sign (~).
  2002, Karen Bromley, Stretching Students' Vocabulary, page 12
  Indicate the comparative value of each heading by keying it with a number in pencil, in the left margin, as follows: […]
  2007, Stephen Blake Mettee, Michelle Doland, and Doris Hall, compilers, The American Directory of Writer's Guidelines, 6th ("2007–2008") edition, page 757
4. (telegraphy and radio telegraphy) To depress (a telegraph key).
5. (radio) To operate (the transmitter switch of a two-way radio).
6. (computing) (more usually to key in) To enter (information) by typing on a keyboard or keypad.
7. (colloquial) To vandalize (a car, etc.) by scratching with an implement such as a key.
8. To link (as one might do with a key or legend).
  Quotations
  The American Heart Association has prepared their own guide to classification and, keying it with the Standard Nomenclature of Diseases, have done much to encourage a concise yet complete diagnosis.
  1960, Richard L. Masland, “Classification of the Epilepsies”, in Epilepsia, volume 1, page 516
  The workman's compensation system rests on incentives (premium payments) that are keyed to the immediate and relatively undeniable nature of injuries; […]
  1976, Nicholas Askounes Ashford, Crisis in the Workplace: Occupational Disease and Injury‎, page 19
  It also features special issues on "Live Longer, Better, Wiser," men's health, women's health, and issues keyed to important "disease weeks."
  2006, Deborah Blum, Mary Knudson, Robin Marantz Henig, A Field Guide for Science Writers: The Official Guide of the National Association of Science Writers‎, page 63
9. (intransitive, biology, chiefly taxonomy) To be identified as a certain taxon when using a key.
10. (advertising, transitive) To modify (an advertisement) so as to target a particular group or demographic.
  Quotations
  Keying advertisements and counting the number of inquiries received or the number of coupons returned to indicate the "pulling power" of a particular piece of copy or the coverage of a particular advertising medium.
  1936, John Freeman Pyle, Marketing Principles, Organization and Policies, page 711
  Another popular way to key ads and mailings is to use a suite number, room number, department number, desk number, etc. as part of the ordering address. With a classified ad, using such a key may increase your ad cost. Why? Because you're using an extra word or two to key the ad.
  1998, Mail Order Success Secrets
11. To attune to; to set at; to pitch.
  Quotations
  To Ethel alone she addressed a stray remark, keyed below the sound of other voices.
  1930, Norman Lindsay, Redheap, Sydney, N.S.W.: Ure Smith, published 1965, page 23
12. To fasten or secure firmly; to fasten or tighten with keys or wedges.
  Quotations
  they Mouldered and keyed the Portico Arches with Pieces of Stone, because Brick was not strong enough
  1744, Roger North, The Life of the Honourable Sir Dudley North
13. To prepare for plastering by adding the key (that part of the plastering which is forced through between the laths and holds the rest in place).
14. To provide an arch with a keystone.
  Quotations
  The last arch in the permanant [sic] bridge was keyed on March 26, 1850, and a single track was brought into use for goods trains on July 20.
  1950 September, “Centenary of the Royal Border Bridge”, in Railway Magazine, page 637

key²

/kiː/

noun
plural keys
1. One of a string of small islands.

key³

/kiː/

noun
plural keys
1. Alternative form of quay.

key⁴

/kiː/

noun
plural keys
1. (slang) Clipping of kilogram (especially of a recreational drug)
  Quotations
  So starting with ten keys of cocaine and two keys of heroin, Derrick put his plan in motion. Soon every major drug dealer and gang chief from Chicago Avenue to Evanston was in his pocket.
  2010, David J. Silas, Da Block, page 41