from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Fraught with uncertainty or doubt; undecided.
  • adjective Arousing doubt; doubtful.
  • adjective Of questionable character.

from The Century Dictionary.

  • Doubting; hesitating; wavering or fluctuating in opinion, but inclined to doubt.
  • Doubtful; marked by or occasioning doubt or uncertainty; difficult to determine or relieve of uncertainty; not distinct or plain; puzzling: as, a dubious question; a dubious light.
  • Of uncertain event or issue: as, a dubious undertaking.
  • Liable to doubt or suspicion; of doubtful quality or propriety; questionable: as, a man of dubious character; a dubious transaction; his morals or his methods are dubious. Synonyms Unsettled, undetermined.
  • Doubtful, Ambiguous, etc. (see obscure, a.); questionable, problematical, puzzling.

from the GNU version of the Collaborative International Dictionary of English.

  • adjective Doubtful or not settled in opinion; being in doubt; wavering or fluctuating; undetermined.
  • adjective Occasioning doubt; not clear, or obvious; equivocal; questionable; doubtful.
  • adjective Of uncertain event or issue.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective Arousing doubt; questionable; open to suspicion.
  • adjective In disbelief; wavering, uncertain, or hesitating in opinion; inclined to doubt; undecided.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adjective open to doubt or suspicion
  • adjective fraught with uncertainty or doubt
  • adjective not convinced


from The American Heritage® Dictionary of the English Language, 4th Edition

[From Latin dubius; see dwo- in Indo-European roots.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Latin dubius.


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  • Irish dubh dark, black. Hence, doubtful?

    January 8, 2009

  • OED etymology of dubious is:

    ad. L. dubis-us doubtful, f. dubium doubt, neuter of dubius doubtful.

    Etymology of doubtful as a noun is:

    ME. a. Of. dute, dote, doute, vbl. n. f. douter to DOUBT. The spelling doute, dought, arose from the spoken identity, which per contra caused DOUGHTY to be spelt doubty. As to the mod. spelling with b, see DOUBT v.

    As a verb is:

    ME. duten, douten, a. OF. duter, doter, douter, (14-16th c. also doubter):L. dubitre to waver in opinion, hesitate, related to dubius wavering to and fro, DUBIOUS. The normal 14th c. forms in Fr. and Eng. were douter, doute; the influence of Latin caused these to be artificially spelt doubt-, which in 17th c. was again abandoned in Fr., but retained in Eng.

    Branch II ‘to fear, to be in fear’, a development of the verb in OF., was an early and very prominent sense of the vb. and its derivatives in ME.: cf. also REDOUBT, etc

    Doesn't look like any of them come from Gaelic.

    January 8, 2009

  • And the Latin root dub- is probably from a contraction of du- "two" + hab- "have", i.e. "be in two minds".

    January 8, 2009