pantsyoudaoicibaDictYouDict[pants 词源字典]
pants: [19] Pants is short for pantaloons, a term used since the 17th century for men’s nether garments. The word originated in the name of a character in the old Italian commedia dell’arte, Pantalone, a silly old man with thin legs who encased them in tight trousers. English took the word over via French pantalon, and began to use it for ‘tight breeches or trousers’.

In American English it broadened out to ‘trousers’ generally, whence the current American use of pants for ‘trousers’. British English, however, tends to use the abbreviation for undergarments, perhaps influenced by pantalets, a 19th-century diminutive denoting ‘women’s long frilly drawers’.
[pants etymology, pants origin, 英语词源]
pants (n.)youdaoicibaDictYouDict
trousers, 1840, see pantaloons. Colloquial singular pant is attested from 1893. To wear the pants "be the dominant member of a household" is first attested 1931. To do something by the seat of (one's) pants "by human instinct" is from 1942, originally of pilots, perhaps with some notion of being able to sense the condition and situation of the plane by engine vibrations, etc. To be caught with (one's) pants down "discovered in an embarrassing condition" is from 1932.