Credible and credulous look similar, but they describe very different things.
Credible means believable, convincing, or worthy of trust. It usually describes a person, explanation, source, or claim that seems reliable. For example, She gave a credible explanation for the delay. You could also say, The witness seemed credible.
Credulous means too ready to believe something, especially without enough evidence. It describes a person who is easily fooled or overly trusting. For example, He was credulous enough to trust the scam.
A useful way to remember the contrast is this: a credible statement should make others believe it, while a credulous person believes things too quickly.
- Use credible for something trustworthy or convincing.
- Use credulous for someone who accepts claims too easily.
If you mean reliable, choose credible. If you mean gullible or easily convinced, choose credulous.