Synonyms for Sheepskin (same or very similar meaning)
WordNet sense 1 (tanned skin of a sheep with the fleece left on; used for clothing):
fleeceWordNet sense 2 (skin of a sheep or goat prepared for writing on):
lambskin, parchmentWordNet sense 3 (a document certifying the successful completion of a course of study):
diplomaFrom the ODE community, based on WordNetadd/edit