layover vs lay over

layover is a noun but lay over is not a noun.

Word	Noun	Adjective	Verb	Adverb
layover	Yes	No	No	No
lay over	No	No	Yes	No

layover (noun)	lay over (noun)
a brief stay in the course of a journey

layover (verb)	lay over (verb)
	place on top of
	interrupt a journey temporarily, e.g., overnight