1.  enthusiast(n = noun.person) partisan, partizan - an ardent and enthusiastic supporter of some person or activity;
is a kind of admirer, booster, champion, friend, protagonist, supporter
has particulars: addict, freak, junkie, junky, nut, backslapper, balletomane, fanatic, fiend, gadgeteer, shutterbug, fan, rooter, sports fan

2.  enthusiast(n = noun.person) fancier - a person having a strong liking for something;
is a kind of admirer, adorer
has particulars: animal fancier, bird fancier, maniac, technophile

   One moved or actuated by enthusiasm; as: (a) One who imagines himself divinely inspired, or possessed of some special revelation; a religious madman; a fanatic. (b) One whose mind is wholly possessed and heated by what engages it; one who is influenced by a peculiar; fervor of mind; an ardent and imaginative person. [1913 Webster]
"Enthusiasts soon understand each other."

enthusiast, n.
1 (often foll. by for) a person who is full of enthusiasm.
2 a visionary; a self-deluded person.

Etymology:
F enthousiaste or eccl.L enthusiastes f. Gk (as ENTHUSIASM)

N  obstinacy, obstinateness, obstinacy, tenacity, cussedness, perseverance, immovability, old school, inflexibility, obduracy, obduration, dogged resolution, resolution, ruling passion, blind side, self-will, contumacy, perversity, pervicacy, pervicacity, indocility, bigotry, intolerance, dogmatism, opiniatry, opiniativeness, fixed idea, fanaticism, zealotry, infatuation, monomania, opinionatedness opinionativeness, mule, opinionist, opinionatist, opiniator, opinator, stickler, dogmatist, bigot, zealot, enthusiast, fanatic, obstinate, tenacious, stubborn, obdurate, casehardened, inflexible, balky, immovable, unshakable, not to be moved, inert, unchangeable, inexorable, mulish, obstinate as a mule, pig-headed, dogged, sullen, sulky, unmoved, uninfluenced unaffected, willful, self-willed, perverse, resty, restive, restiff, pervicacious, wayward, refractory, unruly, heady, headstrong, entete, contumacious, crossgrained, arbitrary, dogmatic, positive, bigoted, prejudiced, creed- bound, prepossessed, infatuated, stiff-backed, stiff necked, stiff hearted, hard-mouthed, hidebound, unyielding, impervious, impracticable, inpersuasible, unpersuadable, intractable, untractable, incorrigible, deaf to advice, impervious to reason, crotchety, obstinately, non possumus, no surrender, ils n'ont rien appris ne rien oublie.

N  activity, briskness, liveliness, animation, life, vivacity, spirit, dash, energy, snap, vim, nimbleness, agility, smartness, quickness, velocity, alacrity, promptitude, despatch, dispatch, expedition, haste, punctuality, eagerness, zeal, ardor, perfervidum aingenium, empressement, earnestness, intentness, abandon, vigor, devotion, exertion, industry, assiduity, assiduousness, sedulity, laboriousness, drudgery, painstaking, diligence, perseverance, indefatigation, habits of business, vigilance, wakefulness, sleeplessness, restlessness, insomnia, pervigilium, insomnium, racketing, movement, bustle, stir, fuss, ado, bother, pottering, fidget, fidgetiness, flurry, officiousness, dabbling, meddling, interference, interposition, intermeddling, tampering with, intrigue, press of business, no sinecure, plenty to do, many irons in the fire, great doings, busy hum of men, battle of life, thick of the action, housewife, busy bee, new brooms, sharp fellow, sharp blade, devotee, enthusiast, zealot, meddler, intermeddler, intriguer, busybody, pickthank, hummer, hustler, live man, rustler, active, brisk, brisk as a lark, brisk as a bee, lively, animated, vivacious, alive, alive and kicking, frisky, spirited, stirring, nimble, nimble as a squirrel, agile, light-footed, nimble-footed, featly, tripping, quick, prompt, yare, instant, ready, alert, spry, sharp, smart, fast, quick as a lamplighter, expeditious, awake, broad awake, go-ahead, live wide-awake, forward, eager, strenuous, zealous, enterprising, in earnest, resolute, industrious, assiduous, diligent, sedulous, notable, painstaking, intent, indefatigable, unwearied, unsleeping, never tired, plodding, hard-working, businesslike, workaday, bustling, restless, restless as a hyena, fussy, fidgety, pottering, busy, busy as hen with one chicken, working, at work, on duty, in harness, up in arms, on one's legs, at call, up and doing, up and stirring, busy, occupied, hard at work, hard at it, up to one's ears in, full of business, busy as a bee, busy as a one-armed paperhanger, meddling, meddlesome, pushing, officious, overofficious, intrigant, astir, stirring, agoing, afoot, on foot, in full swing, eventful, on the alert, actively, with life and spirit, with might and main &c, with haste, with wings, full tilt, in mediis rebus, Int, be alive, look alive, look sharp!, move on, push on!, keep moving!, go ahead!, stir your stumps!, age quod agis!, jaldi!, karo!, step lively!, carpe diem, seize the day, nulla dies sine linea, nec mora nec requies, the plot thickens, No sooner said than done, veni vidi vici, catch a weasel asleep, abends wird der Faule fleissig, dictum ac factum, schwere Arbeit in der Jugend ist sanfte Ruhe im Al, hard work in youth means soft rest in age, the busy hum of men.

N  madman, lunatic, maniac, bedlamite, candidate for Bedlam, raver, madcap, crazy, energumen, automaniac, monomaniac, dipsomaniac, kleptomaniac, hypochondriac (low spirits), crank, Tom o'Bedlam, dreamer, rhapsodist, seer, highflier, enthusiast, fanatic, fanatico, exalte, knight errant, Don Quixote, idiot.