cave in vs slide down

cave in is a noun but slide down is not a noun.

Word	Noun	Adjective	Verb	Adverb
cave in	Yes	No	Yes	No
slide down	No	No	Yes	No

As verbs, slide down is a hyponym of cave in; that is, slide down is a word with a more specific, narrower meaning than cave in:

Other hyponyms of cave in include go off, implode, buckle, crumple, flop, break, sink, slump.

cave in (noun)	slide down (noun)
the sudden collapse of something into a hollow beneath it

cave in (verb)	slide down (verb)
break down, literally or metaphorically	fall or sink heavily