Synonyms for Skeptical (same or very similar meaning)
WordNet sense 1 (marked by or given to doubt):
questioning, doubting, scepticalWordNet sense 2 (denying or questioning the tenets of especially a religion):
disbelieving, unbelievingWordNet sense 3 (not disposed or willing to believe; unbelieving):
incredulousFrom the ODE community, based on WordNetadd/edit