1760, "young dog," shortened form of puppy (q.v.). Used earlier (from 1580s) for "conceited person," from the figurative sense of puppy. An English-Latin wordbook from late 15c. for Latin pupa gives English pup-bairn. Applied to the young of the fur seal from 1815. Used for "inexperienced person" by 1890.
Pup tent (also dog tent) as a type of small tent used in the military is from 1863. Sopwith pup, popular name of the Sopwith Scout Tractor airplane, is from 1917.
"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]