trousers

Attested since the 1610s, from the earlier form trouzes (attested since the 1580s), extended from trouse (1570s), with plural ending typical of things in pairs, from Middle Irish triubus (“close-fitting shorts”), from Old Irish tribus, of uncertain origin. The unexplained intrusive second -r- is perhaps due to the influence of drawers. Doublet of trews (“trousers”).

Old Irish tribus is probably a borrowing of Anglo-Norman tribuz, trebuz, from Old French trebus, from Old Occitan trebucs, trabucs, from Late Latin trabrugi, tribuces, tubruci (“leg-coverings”), from an early Germanic language, perhaps Gothic *𐌸𐌹𐌿𐌷𐌱𐍂𐍉𐌺𐍃 (*þiuhbrōks) or Old High German diohbruoh (“loincloth, trousers”), ultimately from Proto-Germanic *þeuhabrōks (“loincloth, trousers”), a compound of Proto-Germanic *þeuhą (“thigh”) + *brōks (“leggings, trousers”), equivalent to thigh +‎ breeches. Compare obsolete Modern German Diechbruch (“short legwear, knee breeches, loincloth”).