cave in vs subsidence

cave in and subsidence both are nouns.

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

As nouns, cave in and subsidence are synonyms defined as:

cave in and subsidence: the sudden collapse of something into a hollow beneath it

cave in (noun)	subsidence (noun)
the sudden collapse of something into a hollow beneath it	a gradual sinking to a lower level
	the sudden collapse of something into a hollow beneath it
	an abatement in intensity or degree (as in the manifestations of a disease)

cave in (verb)	subsidence (verb)
break down, literally or metaphorically