parchment: [13] Under several layers of disguise lurks the geographical origin of parchment: the ancient town of Pergamum in western Turkey, whose inhabitants used the skin of sheep for writing on rather than papyrus. In Latin, such skin was known as charta Pergamīna ‘paper from Pergamum’, or simply pergamīna. This was later blended with Parthica pellis ‘Parthian leather’ to produce a Vulgar Latin *particamīnum, which passed into English via Old French parchemin (the ending was changed to -ment on the model of other English words, in the 15th century).
The formal distinction between parchment (made from sheepskin) and vellum (made from calfskin) has never been particularly watertight in English. [parchment etymology, parchment origin, 英语词源]