DUBIOUS
doubtful, dubious
(adjective) fraught with uncertainty or doubt; “they were doubtful that the cord would hold”; “it was doubtful whether she would be admitted”; “dubious about agreeing to go”
dubious
(adjective) not convinced; “they admitted the force of my argument but remained dubious”
doubtful, dubious, dubitable, in question
(adjective) open to doubt or suspicion; “the candidate’s doubtful past”; “he has a dubious record indeed”; “what one found uncertain the other found dubious or downright false”; “it was more than dubitable whether the friend was as influential as she thought”- Karen Horney
Source: WordNet® 3.1
Etymology
Adjective
dubious (comparative more dubious, superlative most dubious)
(of a statement) Arousing doubt; questionable; open to suspicion.
(of a person) In disbelief; wavering, uncertain, or hesitating in opinion; inclined to doubt; undecided.
Usage notes
Largely synonymous with doubtful, when used of statements or facts, dubious is used when the statement is a cause of doubt, while doubtful is used when a fact is in doubt. For example, “the company’s earnings report was dubious” vs. “his chances for recovery are doubtful”.
Source: Wiktionary
Du"bi*ous, a. Etym: [L. dubius, dubiosus, fr. duo two. See Two, and
cf. Doubt.]
1. Doubtful or not settled in opinion; being in doubt; wavering or
fluctuating; undetermined. "Dubious policy." Sir T. Scott.
A dubious, agitated state of mind. Thackeray.
2. Occasioning doubt; not clear, or obvious; equivocal; questionable;
doubtful; as, a dubious answer.
Wiping the dingy shirt with a still more dubious pocket handkerchief.
Thackeray.
3. Of uncertain event or issue; as, in dubious battle.
Syn.
– Doubtful; doubting; unsettled; undetermined; equivocal;
uncertain. Cf. Doubtful.
Source: Webster’s Unabridged Dictionary 1913 Edition