Unlikely

wiktionary

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From Middle English unlykely, unlikly, unlykly, unlicli, equivalent to un- +‎ likely.

etymonline

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unlikely (adj.)

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 (adv.)

mid-15c., "improbably," from un- (1) "not" + likely (adv.) (see likely (adj.)).