doublet
n
1 (formerly) short close-fitting jacket worn by men, with or without sleeves (舊時)男用緊身上衣或背心.
2 either of a pair of similar things, esp one of two words with the same origin but a different form or meaning, eg hospital/hostel 一對類似的東西中的一個; (尤指同源異形或異義的)雙式詞, 如hospital/hostel.