Merriam-Webster Collegiate Dictionary - credential

 I. adjective  Date: 15th century warranting credit or confidence — used chiefly in the phrase ~ letters  II. noun  Date: 1655  1. something that gives a title to credit or confidence; also qualification 3a  2. plural testimonials or certified documents showing that a person is entitled to credit or has a right to exercise official power  3. certificate, diploma  III. transitive verb  (-tialed; also -tialled; -tialing; also -tialling)  Date: 1888 to furnish with ~s to ~ adequate academic performance — K. Patricia Cross