diploma

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A document issued by an educational institution, such as a university, testifying that the recipient has earned a degree or has successfully completed a particular course of study.
• noun A certificate conferring a privilege or honor.
• noun An official document or charter.

from The Century Dictionary.

• To furnish with a diploma; certify by a diploma.
• noun Originally, a letter or other composition written on paper or parchment and folded.
• noun Hence Any letter, literary muniment, or public document. See diplomatics.
• noun In modern use, a letter or writing, usually under seal and signed by competent authority, conferring some honor, privilege, or power, as that given by a college in evidence of a degree, or authorizing a physician to practise his profession, and the like.

from the GNU version of the Collaborative International Dictionary of English.

• noun A letter or writing, usually under seal, conferring some privilege, honor, or power; a document bearing record of a degree conferred by a literary society or educational institution.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A document issued by an educational institution testifying that the recipient has earned a degree or has successfully completed a particular course of study.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a document certifying the successful completion of a course of study