underfur vs fur

underfur and fur both are nouns.

Word	Noun	Adjective	Verb	Adverb
underfur	Yes	No	No	No
fur	Yes	No	No	No

As nouns, fur is a hypernym of underfur; that is, fur is a word with a broader meaning than underfur:

underfur: thick soft fur lying beneath the longer and coarser guard hair
fur: dense coat of fine silky hairs on mammals (e.g., cat or seal or weasel)

underfur (noun)	fur (noun)
thick soft fur lying beneath the longer and coarser guard hair	dense coat of fine silky hairs on mammals (e.g., cat or seal or weasel)
	a garment made of animal pelts or synthetic fur
	the dressed hairy coat of a mammal