Definition of "onion"

onion

/ˈʌn.jən/

noun
plural onions
1. A monocotyledonous plant (Allium cepa), allied to garlic, used as vegetable and spice.
2. The bulb of such a plant.
  Quotations
  dorrẹ̅, dōrī adj. & n. […] cook. glazed with a yellow substance; pome(s ~, sopes ~. […] 1381 Pegge Cook. Recipes p. 114: For to make Soupys dorry. Nym onyons […] Nym wyn […] toste wyte bred and do yt in dischis, and god Almande mylk.
  1962 (quoting 1381 text), Hans Kurath & Sherman M. Kuhn, eds., Middle English Dictionary, Ann Arbor, Mich.: University of Michigan Press, ISBN 978-0-472-01044-8, page 1242
3. A plant of the genus Allium as a whole.
4. (slang, of a drug) An ounce.
5. (obsolete baseball slang) A ball.
6. (obsolete, slang) A watch-seal.
  Quotations
  […] M was a Magsman, frequenting Pall-Mall; / N was a Nose that turned chirp on his pal; / O was an Onion, possessed by a swell; / P was a Pannie, done niblike and well. […]
  1846, George William MacArthur Reynolds, The Mysteries of London, page 60
7. Alternative letter-case form of Onion (“an inhabitant of Bermuda; a Bermudian”)