catch some Z's vs slumber

catch some Z's is not a noun while slumber is a noun.

Word	Noun	Adjective	Verb	Adverb
catch some Z's	No	No	Yes	No
slumber	Yes	No	Yes	No

As verbs, catch some Z's and slumber are synonyms defined as:

Other synonyms of catch some Z's include kip, log Z's, sleep.

catch some Z's (noun)	slumber (noun)
	a dormant or quiescent state
	a natural and periodic state of rest during which consciousness of the world is suspended

catch some Z's (verb)	slumber (verb)
be asleep	be asleep