n.1 a liliaceous plant, Allium cepa, having a short stem and bearing greenish-white flowers.
2 the swollen bulb of this with many concentric skins used in cooking, pickling, etc.
Phrases and idioms:
know one's onions be fully knowledgeable or experienced. onion dome a bulbous dome on a church, palace, etc. onion-skin
1. the brown outermost skin or any outer skin of an onion.
2 thin smooth translucent paper.
Derivatives:
oniony adj.
Etymology: ME f. AF union, OF oignon ult. f. L unio -onis