unlikely (adj.)youdaoicibaDictYouDict[unlikely 词源字典]
late 14c., "not likely to occur," from un- (1) "not" + likely (adj.). Similar formation in Old Norse ulikligr, Middle Danish uligelig. Meaning "not likely to be true" is recorded from 1590s. Related: Unlikeliness; unlikelihood.[unlikely etymology, unlikely origin, 英语词源]
unlikely (adv.)youdaoicibaDictYouDict
mid-15c., "improbably," from un- (1) "not" + likely (adv.) (see likely (adj.)).