Definition of "accidental"

accidental

/ˌæk.sɪ.ˈdɛn.tl̩/

adjective
comparative more accidental, superlative most accidental
1. Pertaining to accident and not essence; thus, inessential; incidental; secondary.
  1. (philosophy) Nonessential to something's inherent nature (especially in Aristotelian thought).
2. (music) Adjusted by one or two semitones, in temporary departure from the key signature.
3. Occurring sometimes, by chance; occasional.
4. Happening by chance, or unexpectedly; taking place not according to the usual course of things; by accident, unintentional.
  Quotations
  The way to trueth is but one and simple, that of particular profit and benefit of affaires a man hath in charge, double, uneven and accidentall [translating fortuite].
  1603, Michel de Montaigne, translated by John Florio, Essays, translation of original in French, III.1
5. (geometry) Being a double point with two distinct tangent planes in 4-dimensional projective space.
noun
plural accidentals
1. A property which is not essential; a nonessential; anything happening accidentally.
  Quotations
  He conceived it just that accidentals ... should sink with the substance of the accusation.
  1662, Fuller, Worthies of England
2. (painting, plural only) Those fortuitous effects produced by luminous rays falling on certain objects so that some parts stand forth in abnormal brightness and other parts are cast into a deep shadow.
3. (music) A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.
4. Part of a text that has a mainly structural purpose, such as spelling, punctuation, or capitalization.