credential (n.)

"that which entitles to credit," 1756, probably a back-formation from credentials, from Medieval Latin credentialis, from credentia "belief," from Latin credere "to believe, trust" (see credo). Rare in the singular form. Earlier in English as an adjective, "confirming, corroborating" (late 15c.). As a verb, "provide with credentials," by 1828 (implied in credentialed).