Synonyms for doubtful

Similarity of adj doubtful

3 senses of doubtful

Sense 1:

doubtful, dubious, dubitable, in question(predicate)
questionable (vs. unquestionable)

Sense 2:

doubtful, dubious
uncertain (vs. certain), unsure (vs. sure), incertain

Sense 3:

doubtful, tentative
unsettled (vs. settled)