= disbelieve, question, challenge, suspect, dispute, query, distrust, mistrust, cast doubt on, have doubts about, lack confidence in, have misgivings about, misgive •
I have no reason to doubt his word.
opposites: believe, accept, trust, buy (slang), swallow (informal), take on board, have faith in
See in doubt
See no doubt
In affirmative sentences, whether was in the past the only word considered acceptable for linking the verb doubt to a following clause, for example I doubt whether he will come. Nowadays, doubt if and doubt that are both considered acceptable alternatives to doubt whether. In negative sentences, use that after doubt, for example I don't doubt that he is telling the truth. The old-fashioned form not doubt but that, as in I do not doubt but that he is telling the truth, is now rarely used and sounds very stiff and formal.