Trousers are what you wear on your legs, with a separate tube for each. Always plural, however many you own.
This is the British word, and Americans say pants, which in Britain means underwear, so the pair causes more confusion than almost any other. You buy a pair of trousers. English gets an idiom about authority from them, since whoever wears the trousers in a household makes the decisions. Being caught with your trousers down means being caught unprepared and embarrassed.
1nountrousersAn outer garment covering the body from the waist down, with a part for each leg.
“He bought a new pair of trousers for the interview.”
Also accepted in games: pants
Trousers came from Irish. Middle Irish triubus meant close-fitting shorts, English took it in as trouse, and the s was added later because that is the ending we give to things that come in pairs.
Proto-Germanic
*þeuhabrōks — loincloth, trousers
Old High German
diohbruoh — loincloth, trousers
Gothic
*𐌸𐌹𐌿𐌷𐌱𐍂𐍉𐌺𐍃
Latin
trabrugi
Old Occitan
trebucs
Old French
trebus
Anglo-Norman
tribuz
Old Irish
tribus
mga
triubus — close-fitting shorts
English, today
trousers
Built from
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 mga triubus (“close-fitting shorts”), from Old Irish tribus, of unknown origin. The unexplained intrusive second -r- is perhaps due to the influence of drawers. a doublet of trews. Old Irish tribus is probably a borrowing of Anglo-Norman tribuz, trebuz, from Old French trebus, from Old Occitan trebucs, trabucs, from Latin trabrugi, tribuces, tubruci (“leg-coverings”), from an early gem - language, perhaps Gothic 𐌸𐌹𐌿𐌷𐌱𐍂𐍉𐌺𐍃 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”).
Etymology from Wiktionary, CC BY-SA