When the word fur first came into English, it was a verb that meant “to line a person’s garment with the soft hair of an animal.” The noun developed from the verb. First, the noun referred to the animal hair that was used for lining and trimming a garment. Then it came to refer to the hairy coat on the animal itself. The verb, not much used anymore, was taken from the early French verb furrer, meaning “to stuff, fill, line.” It was formed from an earlier French word meaning “a sheath.” Thus our word fur for the hairy coat that covers or encases an animal traces back to a word for a sheath that encases a knife or sword.