underfelt vs underlay

underfelt and underlay both are nouns.

Word	Noun	Adjective	Verb	Adverb
underfelt	Yes	No	No	No
underlay	Yes	No	Yes	No

As nouns, underlay is a hypernym of underfelt; that is, underlay is a word with a broader meaning than underfelt:

Other hypernyms of underfelt include carpet pad, rug pad, underlayment.

underfelt (noun)	underlay (noun)
a carpet pad of thick felt	a pad placed under a carpet

underfelt (verb)	underlay (verb)
	provide with a base, support, lining, or backing
	put (something) under or beneath
	raise or support (the level of printing) by inserting a piece of paper or cardboard under the type