Synonyms for Dubious (same or very similar meaning)
WordNet sense 1 (open to doubt or suspicion):
doubtful, dubitableWordNet sense 2 (subject to question):
questionableWordNet sense 3 (lacking conviction):
unconvincedWordNet sense 4 (lacking or indicating lack of confidence or assurance):
uncertain, unsure, incertainFrom the ODE community, based on WordNetadd/edit