1. Roman law. A letter giving permission to use the imperial post.
2. Hist. A royal charter; letters patent.
3. A document that evidences or memorializes graduation from a school or society. Cf. DEGREE(6). [Cases: Schools 178. C.J.S. Schools and School Districts §§ 803–806.]
4. A document that evidences a license or privilege to practice a profession, such as medicine.