onion

[ uhn-yuh n ]
/ ˈʌn yən /

noun

adjective

containing or cooked with onions: onion soup.
of, relating to, or resembling an onion.

Idioms for onion

    know one's onions, Slang. to know one's subject or business thoroughly; be capable or proficient.

Origin of onion

1325–75; Middle English onyon < Old French oignon < Latin ūniōn- (stem of ūniō) a unity, large pearl, onion; see union

OTHER WORDS FROM onion

on·ion·like, adjectiveon·ion·y, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for know one's onions

onion
/ (ˈʌnjən) /

noun

an alliaceous plant, Allium cepa, having greenish-white flowers: cultivated for its rounded edible bulb
the bulb of this plant, consisting of concentric layers of white succulent leaf bases with a pungent odour and taste
any of several related plants similar to A. cepa, such as A. fistulosum (Welsh onion)
know one's onions British slang to be fully acquainted with a subject

Derived forms of onion

oniony, adjective

Word Origin for onion

C14: via Anglo-Norman from Old French oignon, from Latin unio onion, related to union
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Idioms and Phrases with know one's onions

onion

see know one's stuff (onions).

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.