"a talisman, charm, thing supposed to bring good luck to its possessor," also "person whose presence is supposed to be a cause of good fortune," 1881, from provincial French mascotte "sorcerer's charm, 'faerie friend,' good luck piece" (19c.), of uncertain origin, perhaps from or related to Provençal mascoto "sorcery, fetish" (a Narbonnese manuscript of 1233 has mascotto "procuress, enchantment, bewitchment in gambling"), from masco "witch," from Old Provençal masca, itself of unknown origin, perhaps from Medieval Latin masca "mask, specter, nightmare" (see mask (n.)).
Popularized by French composer Edmond Audran's 1880 comic operetta "La Mascotte," about a household "fairy" who gives luck to an Italian peasant, which was performed in a toned-down translation in England from fall 1881. In reference to animals (later costumed characters) representing sports teams, by 1889.
For the edification of readers not versed in baseball lore it should be stated that the mascot has become quite an important institution among the professional teams of America. He may be a boy possessed of some special attainment or physical peculiarity, or he may be a bull-pup with a prominent patch over his left eye. It matters not whether a mascot be brute or human, so long as his presence upon the players' bench insures a victory—in the minds of the players—to the team with which he has cast his fortunes and in whose favor he exercises the influence he is supposed to have with Dame Fortune. [Harry Clay Palmer, ed., "Athletic Sports in America, England, and Australia," New York, 1889]
Old English gat "she-goat," from Proto-Germanic *gaito (source also of Old Saxon get, Old Norse geit, Danish gjed, Middle Dutch gheet, Dutch geit, Old High German geiz, German Geiß, Gothic gaits "goat"), from PIE *ghaid-o- "young goat," also forming words for "to play" (source also of Latin hædus "kid").
They are sprightly, capricious, and wanton, and their strong odor (technically called hircine) is proverbial. [Century Dictionary]
The word for "male goat" in Old English was bucca or gatbucca (see buck (n.)) until late 1300s shift to he-goat, she-goat (Nanny goat is 18c., billy goat 19c.). Meaning "licentious man" is attested from 1670s (hence goat-milker, name of a bird formerly believed to suck the milk from goats at night, but also old slang for "a prostitute," also "the female pudendum"). To get (someone's) goat is by 1908, American English, the source of many fanciful explanation stories; perhaps from French prendre sa chèvre "take one's source of milk," or more likely it is "to steal a goat mascot" from a racehorse, warship, fire company, military unit, etc.
... to become separated from your goat is a thing no soldierman is willing to contemplate. ["Letitia, Nursery Corps, U.S.A.," in American Magazine, vol. lxiv, June 1907]