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to doubt; to distrust; to be suspicious of; to suspect
彼の言うことを疑う理由は何もなかった。
There was no reason to doubt what he said.
彼女は最初から彼を疑っていた。
She had been doubting him from the beginning.
自分の目を疑うような光景だった。
It was a sight that made me doubt my own eyes.