Synonym: dubious, dubitable, in question, tentative. Similar words: doubt, no doubt, without doubt, undoubtedly, fretful, double, frightful, deceitful. Meaning: ['daʊtfʊl] 
adj. 1. open to doubt or suspicion 2. fraught with uncertainty or doubt 3. unsettled in mind or opinion.
adj. 1. open to doubt or suspicion 2. fraught with uncertainty or doubt 3. unsettled in mind or opinion. 
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(61) It is doubtful that voters will approve the bill.
(62) But whether he retains his title may be doubtful.
(63) Whether these figures are statistically significant is doubtful.
(64) Defensive lineman Young is also listed as doubtful.
(65) But already the whole scheme was looking increasingly doubtful.
(66) I could see that Holmes still looked doubtful.
(67) Bruno was doubtful whether you'd even notice the difference.
(68) Doblado accepted the doubtful honor of organizing the fund-raiser.
(69) It means more doubtful inward investment.
(70) It seems doubtful that much planning was necessary.
(71) Nutty was far from sure,(sentencedict.com) and Biddy looked doubtful.
(72) All these doubtful cases are small craters.
(73) It was very doubtful that she would spend next Christmas here.
(74) Rain, Oliver and Cobalt all gave Tim rather doubtful looks.
(75) To outsiders it seemed that the regime was becoming unstable and that its survival appeared more and more doubtful.
(76) This not withstanding,[http://sentencedict.com/doubtful.html] it is doubtful that pit culture is on the brink of extinction.
(77) The real danger lies in a too enthusiastic recording of very doubtful features as marine terraces.
(78) Once on the strip, it is doubtful that the sort of support equipment it is used to will be found there.
(79) It is doubtful whether many would dispute Honderich's first two points.
(80) Candy would be no match for him - it was doubtful if many women would be.
(81) Yet it is doubtful whether Baldwin was in fact wasting time.
(82) But it seems doubtful if it was big enough to have much impact.
(83) Brown said. Defensive lineman Young is also listed as doubtful.
(84) It is doubtful whether the budget will be passed before the elections in July.
(85) I was a bit doubtful at first, but it turned out to be a really good idea.
(86) A doubtful friend is worse than a certain enemy. Let a man be one thing or the other, and we then know how to meet him. Aesop 
(87) They were mostly used to discriminate between doubtful grammar school entrants.
(88) In the current economic climate it is not justifiable to provide screening services of doubtful value.
(89) It is, however, doubtful whether this genuinely represents the ideas circulating in 1483.
(90) Whether such a process can operate on a large enough scale to produce major oasis depressions is more doubtful.
More similar words: doubt, no doubt, without doubt, undoubtedly, fretful, double, frightful, deceitful, double up, delightful, at full speed, double back, double-dealing, double jeopardy, subtle, subterfuge, trouble, troubled, dour, do up, troublesome, hand out, dough, hold out, weed out, washed out, in and out, find out, stand out, send out.