The antonyms for the word "was credulous" are skeptical, doubtful, suspicious, cynical, disbelieving, and incredulous. These words describe a lack of trust in someone or something, rather than a willingness to believe without evidence. If someone is skeptical, they might require proof before believing something. If someone is doubtful, they might have reservations about the truthfulness of a claim. If someone is suspicious, they might be wary of being deceived. If someone is cynical, they might doubt the sincerity of others. If someone is disbelieving, they might outright reject a claim as untrue. If someone is incredulous, they might find a claim too unbelievable to be true.