justifiable (adj.)youdaoicibaDictYouDict[justifiable 词源字典]
1520s, from Old French justifiable, from justifiier (see justify). Earlier in same sense was justificable (mid-15c.). Related: Justifiably (mid-15c.).[justifiable etymology, justifiable origin, 英语词源]
justly (adv.)youdaoicibaDictYouDict
early 14c., "in an adjacent position, closely," from just (adj.) + -ly (2). Meanings "truthfully, honestly," "in an equitable manner, with justice, fairly" are from late 14c. Sense of "justifiably, with good reason" is from c. 1400; that of "legally, legitimately, rightfully" is early 15c.
unjustifiable (adj.)youdaoicibaDictYouDict
1640s, from un- (1) "not" + justifiable. Related: Unjustifiably.