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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(1) He was doubtful about accepting extra work.
(2) It is doubtful that he will come.
(3) Rose was doubtful about the whole idea.
(4) I am doubtful whether she is still alive.
(5) Prospects for a lasting peace remain doubtful.
(6) Eric was far from sure and Marion looked doubtful.
(7) It is doubtful whether the patient will last out this month.
(8) For a time it seemed doubtful that he would move at all.
(9) I am very doubtful of that.
(10) At first we were doubtful about employing Charlie.
(11) She was doubtful about the interview from the off.
(12) Here the tap water is of doubtful quality.
(13) I feel very doubtful about this.
(14) I'm doubtful where to go.
(15) I'm still doubtful whether I should accept this job.
(16) I feel doubtful what I ought to do. Sentencedict.com
(17) It is doubtful whether it is true or not.
(18) Why did he sound so doubtful?
(19) Already the whole scheme was looking increasingly doubtful.
(20) It's doubtful whether the car will last another year.
(21) A doubtful look crossed his face.
(22) The results are of doubtful validity.
(23) The ethics of his decision are doubtful.
(24) It's doubtful if this painting is a Picasso.
(25) This is a doubtful battle.
(26) It's doubtful whether there'll be any seats left.
(27) It is extremely doubtful that anyone survived the explosion.
(28) This wine is of doubtful quality.
(29) He is a doubtful character.
(30) Ecologists argue that the benefits of treating sewage with disinfectants are 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.