fur: [14] Old English did not have a distinct word for ‘animal’s hair’ – the nearest approach to it was fell ‘animal’s hide’. Then in the 13th century English acquired the verb fur ‘line with fur’ from Anglo-Norman *furrer or Old French forrer ‘encase, line’. These were derivatives of the Old French noun forre ‘sheath, case’, a loanword from prehistoric Germanic *fōthram ‘sheath’, which in turn goes back to the Indo-European base *pō- ‘protect’.
In the 14th century the new English verb was taken as the basis for a noun, which originally meant ‘trimming for a garment, made from fur’, or more loosely ‘garment made from fur’; it was not until the 15th century that it was used for ‘animal’s hair’. [fur etymology, fur origin, 英语词源]