WordNet (r) 3.0 (2006):
hobbyist n 1: a person who pursues an activity in their spare time for pleasureMoby Thesaurus II by Grady Ward, 1.0:
20 Moby Thesaurus words for "hobbyist": addict, bug, collector, demon, eager beaver, energumen, enthusiast, faddist, fanatic, fiend, freak, great one for, hound, infatuate, nut, pursuer, rhapsodist, sucker for, visionary, zealot