An Etymological Dictionary of Astronomy and Astrophysics

A plant, Allium cepa, of the amaryllis family, having an edible, succulent, pungent bulb (Dictionary.com).

Etymology (EN): M.E., from Anglo-French union, O.Fr. oignon “onion,” from L. unio-, also “pearl,” literally “one, unity;” sense connection is the successive layers of an onion.

Etymology (PE): Mid.Pers. payâz, payâc; cf. Sogd. piyâk “onion,” Yidgha piq, Vakhi piûk, Yazghulami piyeq, Kurd. pivaz; maybe related to PIE *peuk- “to prick, to sting, to stab,” because of its pungent taste;
cf. Gk. peukos “sting, prick, cusp, peak.”