1620s, "small horse," from French bidet (16c.), of unknown etymology. Originally in French "a small horse, a pony," thus "a vessel on a low narrow stand, which can be bestridden for bathing purposes," a sense attested in English from 1766.
bicyclist
bid
bidden
biddy
bide
bidet
bidirectional
Biedermeier
biennial
biennium
bier