c.1205, a double plural, from O.E.
brec, which was already pl. of
broc "garment for the legs and trunk," from P.Gmc.
*brokiz (cf. O.N.
brok, Du.
broek, O.H.G.
bruoh, Ger.
Bruch, obsolete since 18c. except in Swiss dialect), perhaps from PIE base
*bhreg- (see
break). The P.Gmc. word is a parallel form to Celt.
*bracca, source (via Gaulish) of L.
braca (cf. Fr.
braies), and some propose that the Gmc. word group is borrowed from Gallo-L. Expanded sense of "part of the body covered by breeches, posterior" led to senses in childbirthing (1673) and gunnery ("the part of a firearm behind the bore," 1575). As the popular word for "trousers" in Eng., displaced in U.S. by
pants c.1840. The
Breeches Bible (Geneva Bible of 1560) so called on account of rendition of Gen. iii.7 (already in Wyclif) "They sewed figge leaues together, and made themselues breeches."
[brich-iz] 
)