Synonyms for Dubious:

adj.

all (adjective)
doubtful.
crooked (adjective)
untruthful.
disreputable (adjective)
infamous, shifty, questionable, notorious, disreputable, ribald, contemptible, dishonorable, shady, louche, risque, nefarious.
doubtful (adjective)
problematic, untrustworthy, undecided, dubitable, undependable, skeptical, shady, uncertain, chancy, indecisive, unconvinced, unclear, unsure, hesitant, unreliable, suspect, iffy, suspicious, questionable.
open (adjective)
in question.
ridiculous (adjective)
poppycock, weird, crazy, silly, ridiculous, laughable, eccentric, bizarre, nonsensical, oddball, comical, preposterous, curious, outlandish, outrageous, grotesque, farcical, foolish, ludicrous, absurd, incredible.
shady (adjective)
shady.
skeptical (adjective)
unbelieving, doubtful, cynical, skeptical, suspicious, incredulous.
unreliable (adjective)
unreliable, questionable, undependable, untrustworthy.
vague, unclear (adjective)
doubtful, problematical.

n.

questioning, inclined to think/believe/agree etc., bewildered, sceptical. suspect, deceitful, unprincipled, cunning, fraudulent, corrupt, devious, unscrupulous, dishonest, untruthful. doubtful (noun)
hesitant, indecisive.
dubious (noun)
in question, questionable, incertain, dubitable, unsure, uncertain, doubtful, unconvinced.
vague (noun)
unclear.

Other synonyms:

deceitful, untruthful, chancy, questioning, devious, dishonest, bewildered, unscrupulous, unprincipled, clouded, fraudulent. iffy, unclear, cunning, inconclusive, problematical. indecisive, problematic. borderline. corrupt. undetermined
undecided.
Other relevant words:
hesitant, chancy, indecisive, unsure, unconvinced, paradoxical, corrupt, questioning, unclear, fraudulent, sceptical, clouded, iffy, borderline, in question, undecided, inconclusive, unprincipled, unscrupulous, dubitable, incertain, devious, problematic, uncertain, problematical, suspect, dishonest.

Usage examples for dubious

  1. While this dubious colloquy was fresh in his thoughts, it chanced that Sylvester De Vine, responding to the invitation he had thrown out at the races, trudged up to the manor to see him. – True and Other Stories by George Parsons Lathrop
  2. Scanlon was impressed; but at the same time there was a dubious look in his eye. – Ashton-Kirk, Criminologist by John T. McIntyre
  3. When she was gone, and they had exchanged that dubious look, Lady Valleys said: I came about Babs. – The Patrician by John Galsworthy