Meaning "good will, kind regard" is from mid-14c. in English; sense of "act of kindness, a kindness done" is from late 14c. Meaning "bias, partiality" is from late 14c. Meaning "thing given as a mark of favor" is from late 15c. Phrase in favor of recorded from 1560s.
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").
personification of the west wind in Roman mythology, from Latin Favonius, which de Vaan suggests is cognate with the god-name Faunus (see faun), from a prehistoric noun meaning "who favors" (see favor (n.)):
This also yields a good semantic motivation: the wind that stimulates vegetation can be called favourable. Favonius was regarded by the Romans as the herald of spring and the start of new vegetation (e.g. Cato Agr. 50.1, Cicero Ver. 5.27, Lucretius 1.11, Vitruvius 2.9.1).
The Latin word is the source (via Old High German phonno, 10c., via Vulgar Latin contraction *faonius) of German Föhn "warm, dry wind blowing down Alpine valleys." Related: Favonian.
"person or thing regarded with especial liking," 1580s, from French favorit, perhaps via Italian favorito, noun use of past participle of favorire, from favore, from Latin favorem "inclination, partiality, support" (see favor (n.)).
Especially, "a person who gains dominant influence over a superior" (1590s). In racing, "one considered most likely to win," attested from 1813. In 17c.-18c. also "small curl hanging loose upon the temple," a frequent feature of a woman's head dress.
As an adjective, "regarded with particular liking, esteem, or preference," by 1711. Favorite son in the figurative sense "noted man who is particularly popular and boasted of in his native area" is by 1788.
As a corresponding noun in the sense of "person who promotes the interests of another," Latin had fautor, hence Old French fauteur, Middle English fautour "an adherent, supporter, follower" (mid-14c.), but it has perished along with its fem. form, fautress.