1733, "an admirer of a fine art, literature, science, etc., one who cultivates an art or literature casually and for amusement," a borrowing of Italian dilettante "lover of music or painting," from dilettare "to delight," from Latin delectare "to allure, delight, charm, please," frequentative of delicere "entice" (see delicious). Originally without negative connotation, "devoted amateur;" the pejorative sense "superficial and affected dabbler" emerged late 18c. by contrast with professional.
1784, "one who has a taste for some art, study, or pursuit, but does not practice it," from French amateur "one who loves, lover" (16c., restored from Old French ameour), from Latin amatorem (nominative amator) "lover, friend," agent noun from amatus, past participle of amare "to love" (see Amy).
The meaning "one who cultivates and participates (in something) but does not pursue it professionally or with an eye to gain" (as opposed to professional) is from 1786; often with disparaging suggestions of "dabbler, dilettante," but not in athletics, where the disparagement shaded the professional, at least formerly. As an adjective, by 1838.