[cre.den.tial] adj (15c): warranting credit or confidence--used chiefly in the phrase credential letters
[2]credential n (ca. 1674) 1: something that gives a title to credit or confidence
2. pl: testimonials showing that a person is entitled to credit or has a right to exercise official power
3: certificate, diploma [3]credential vt -tialed also -tialled ; -tial.ing also -tial.ling (1888): to furnish with credentials "to ~ adequate academic performance --K. Patricia Cross"