Someone who habitually doubts accepted beliefs.

synonyms: sceptic, skeptic.

Roget 485: unbelief, disbelief, misbelief; discredit, miscreance^†; infidelity etc. (irreligion) 989^†; dissent etc. 489; change of opinion etc. 484; retraction etc. 607.    doubt etc. (uncertainty) 475; skepticism, scepticism, misgiving, demure; distrust, mistrust, cynicism; misdoubt^†, suspicion, jealousy, scruple, qualm; onus probandi [Lat.].    incredibility, incredibleness; incredulity.    [person who doubts] doubter, skeptic, cynic.   ; unbeliever etc. 487.    ... show more

Dutch: scepticus
Polish: sceptyk

Someone who is doubtful or noncommittal about something.

synonym: agnostic.

Polish: agnostyk