c. 1200, "wickedly; with hostility," from ill (adj.). Meaning "not well, poorly" also is from c. 1200. It generally has not shifted to the realm of physical sickness, as the adjective has done. Ill-fated recorded from 1710; ill-informed from 1824; ill-tempered from c. 1600; ill-starred from c. 1600. Generally contrasted with well, hence the useful, but now obsolete or obscure illcome (1570s), illfare (c. 1300), and illth.
1725, "enjoying unusual advantages," past-participle adjective from favor (v.). In compounds or phrases, "-featured, -looking," from c. 1400 (for example, well-favored "good-looking;" worst-favored "ugliest").
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Harper, D. (n.d.). Etymology of ill-favored. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/ill-favored