gusset (n.)youdaoicibaDictYouDict[gusset 词源字典]
early 14c., from Old French gosset "armhole; piece of armor for the armpit" (13c.), apparently from gousse "shell of a nut," a word of unknown origin. Originally an armorer's term; of clothing from 1560s.[gusset etymology, gusset origin, 英语词源]