The root that means "trust" or "believe" is "cred." It comes from the Latin root "credere," which means "to trust" or "to believe." Many English words related to belief or trust, such as "credit," "credible," and "creed," derive from this root.

Additionally, the English word "trust" itself is linked to the Old Norse root "traust," related to firmness and reliability, but specifically for the given roots, "cred" is the one associated with trust or belief.