credential

Concise Oxford English Dictionary © 2008 Oxford University Press:
credential /krɪˈdɛnʃ(ə)l/

▶noun

• 1 a qualification, achievement, etc., especially when used to indicate a person's suitability for something.

• 2 a letter of introduction given by a government to an ambassador before a new posting.

– derivatives
credentialed adjective (chiefly N. Amer.).

– origin ME (as an adj.): from med. L. credentialis, from credentia (see credence).