collapse vs cave in

collapse and cave in both are nouns.

Word	Noun	Adjective	Verb	Adverb
collapse	Yes	No	Yes	No
cave in	Yes	No	Yes	No

As nouns, cave in is a hyponym of collapse; that is, cave in is a word with a more specific, narrower meaning than collapse:

collapse: a natural event caused by something suddenly falling down or caving in
cave in: the sudden collapse of something into a hollow beneath it

Other hyponyms of collapse include subsidence, debacle, fiasco, implosion.

As verbs, collapse and cave in are synonyms defined as:

Other synonyms of collapse include break, fall in, founder, give, give way.

collapse (noun)	cave in (noun)
the act of throwing yourself down; collapse; sink	the sudden collapse of something into a hollow beneath it
a natural event caused by something suddenly falling down or caving in
a sudden large decline of business or the prices of stocks (especially one that causes additional failures)
an abrupt failure of function or complete physical exhaustion

collapse (verb)	cave in (verb)
collapse due to fatigue, an illness, or a sudden attack	break down, literally or metaphorically
lose significance, effectiveness, or value
suffer a nervous breakdown
break down, literally or metaphorically
fold or close up
fall apart
cause to burst