From Longman Dictionary of Contemporary Englishdoubtfuldoubt‧ful /ˈdaʊtfəl/ ●●○ adjective 1 DON'T THINK SO/DOUBT ITprobably not true or not likely to happen Prospects for a lasting peace remain doubtful.it is doubtful if/whether It was doubtful whether the patient would survive the operation.it is doubtful that It is doubtful that the missing airmen will ever be found.2 NOT SUREnot sure that something is true or right ‘Everything’s going to be all right, you’ll see.’ Jenny looked doubtful.doubtful if/whether I’m still doubtful whether I should accept this job.doubtful about (doing) something At first we were doubtful about employing Charlie.3 unlikely to be successful Already the whole scheme was looking increasingly doubtful.4 UNCERTAINprobably not good SYN dubious Here the tap water is of doubtful quality. —doubtfully adverb
Examples from the Corpusdoubtful• Most local NGOs are dependent on donor funds; their sustainability without such funds is doubtful.• I could see that Holmes still looked doubtful.• But the result confirmed that building society provisions will rocket this year to cover bad and doubtful home loans.• Doblado accepted the doubtful honor of organizing the fund-raiser.• It means more doubtful inward investment.• The general expressed his concern about the number of citizens with doubtful loyalties.• He saw they were doubtful now that this had been a serious meeting.• "Is Maddy coming tonight?" "It's looking doubtful - she was really sick."• Though it was doubtful that Fen's company was any less disturbing.• It's doubtful that we'll finish this tonight.• It is doubtful whether the diners actually find these offerings delicious.• And, of course, it was doubtful whether the girl would back him up.it is doubtful that• Cases were ascertained from multiple sources, and it is doubtful that any were missed, although we can not be certain.• Even in that case, though, it is doubtful that Black could have obtained serious winning prospects.• This not withstanding, it is doubtful that pit culture is on the brink of extinction.• In the case of the database project, it is doubtful that the machine-readable data would be of any use whatsoever.• Once on the strip, it is doubtful that the sort of support equipment it is used to will be found there.• If indeed they were prehistoric, it is doubtful that they crossed the open downland after the later Bronze Age.• It is doubtful that voters will approve the bill.doubtful about (doing) something• Mr. Curry I am somewhat doubtful about a concrete policy for hedgerows.• You have been doubtful about all of this new physics, Watson.• When he heard this, Oliver felt rather doubtful about having such a friend.• With Lord Jim and Grace both on his books, Pinkie felt doubtful about his chance of selling either.• There was nothing doubtful about Mrs Whosis downstairs, except her natural curiosity.• If you are at all doubtful about the success of the evening, do not advertise the event outside your Law Society.• You couldn't have expected it, he had been doubtful about this day from the beginning.