questionable (adj.)youdaoicibaDictYouDict[questionable 词源字典]
1580s, "that may be interrogated;" c. 1600, "open to dispute, doubtful," from question (v.) + -able. Deprecatory sense of "dubious in character" is attested from 1806. Related: Questionably.[questionable etymology, questionable origin, 英语词源]