Synonym: challenge, dispute, mistrust, question, suspect. Similar words: no doubt, without doubt, double, double up, double back, subtle, trouble, troubled. Meaning: [daʊt] 
n. 1. the state of being unsure of something 2. uncertainty about the truth or factuality of existence of something. v. 1. consider unlikely or have doubts about 2. lack confidence in or have doubts about.
n. 1. the state of being unsure of something 2. uncertainty about the truth or factuality of existence of something. v. 1. consider unlikely or have doubts about 2. lack confidence in or have doubts about. 
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(271) No doubt many will regard these as harsh words, but regrettably they are true.
(272) His behaviour was so strange that I began to doubt his sanity.
(273) I have tried to give some idea of how I feel-other people will no doubt draw their own conclusions.
(274) 'You might be wrong, of course!' 'It's possible, but I doubt it.'
More similar words: no doubt, without doubt, double, double up, double back, subtle, trouble, troubled, dour, do up, dough, hand out, hold out, in and out, weed out, stand out, send out, find out, washed out, spread out, tremendous.