Definition of "senior"

senior

/ˈsinjɚ/

adjective
comparative more senior, superlative most senior
1. Older; superior
2. Higher in rank, dignity, or office.
3. (US) Of or pertaining to a student's final academic year at a high school (twelfth grade) or university.
noun
plural seniors
1. (now chiefly US) An old person.
  Quotations
  Grave and reverend seniors seemed to have caught the prevailing spirit as badly as the students, and I saw white-bearded men rising and shaking their fists at the obdurate Professor.
  1912, Arthur Conan Doyle, “‘Question!’”, in The Lost World […], London, New York, N.Y.: Hodder and Stoughton, page 77
2. Someone older than someone else (with possessive).
3. Someone seen as deserving respect or reverence because of their age.
4. (obsolete, biblical) An elder or presbyter in the early Church.
  Quotations
  Then Peter full of the holy gooſt ſayd vnto them. Ye ruelars of the people / and ſeniours of iſrahel […].
  1526, [William Tyndale, transl.], The Newe Testamẽt […] (Tyndale Bible), [Worms, Germany: Peter Schöffer], Acts :, folio clviij, recto
5. Somebody who is higher in rank, dignity, or office.
6. (US, Philippines) A final-year student at a high school or university.