unsweetened (n.)youdaoicibaDictYouDict[unsweetened 词源字典]
1775, "not having been sweetened," from un- (1) "not" + past participle of sweeten (v.); or else, if the sense is "with sweetness removed," from unsweeten (v.), which is attested from 1610s.[unsweetened etymology, unsweetened origin, 英语词源]