credentials (n.)

"letters entitling the bearer to certain credit or confidence," 1670s, from Medieval Latin credentialis, from credentia  "belief," from Latin credere "to believe, trust" (see credo). Probably immediately as a shortening of letters credential (1520s, with French word order); earlier was letter of credence (mid-14c.). Especially in reference to the letters of authorization given by a government to an ambassador.