Definition of doubtful adjective from the Oxford Advanced American Dictionary

     

    doubtful

     adjective
    adjective
    NAmE//ˈdaʊtfl//
     
     
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  1. 1(of a person) not sure; uncertain and feeling doubt synonym dubious doubtful (about something) Rose was doubtful about the whole idea. doubtful (about doing something) He was doubtful about accepting extra work.
  2. 2 unlikely doubtful (if…) It's doubtful if this painting is a Picasso. doubtful (that…) With her injuries ,it's doubtful that she'll ever walk again. doubtful (whether…) It's doubtful whether the car will last another year. doubtful (for something) He is injured and is doubtful for the game tomorrow (= unlikely to play).
  3. 3[not usually before noun] (of a thing) uncertain and likely to get worse At the beginning of the war things were looking very doubtful.
  4. 4[only before noun] of low value; probably not genuine or of a quality that you can rely on synonym dubious This wine is of doubtful quality.
NAmE//ˈdaʊtfəli//
 
adverb
See the Oxford Advanced Learner's Dictionary entry: doubtful