favoritism (n.)

"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.

word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.