unthrifty (adj.)youdaoicibaDictYouDict[unthrifty 词源字典]
late 14c., "unprofitable, useless," from un- (1) "not" + thrifty (adj.), or else from Middle English noun unthrift "profligacy," late 14c., earlier "evil practice, wicked act" (c. 1300).[unthrifty etymology, unthrifty origin, 英语词源]