onion [LME] Onions have been part of the vegetable garden since medieval times, and the name comes ultimately from Latin where it was the word for a large pearl, but used in non-standard speech for a particular variety of onion, distinctive for having a single form that did not put out shoots. To know your onions is to be very knowledgeable about something. The phrase was first used in the USA in the 1900s. There have been many theories about the origins of the expression, but none has been definitively convincing.