subsidence vs cave in

subsidence and cave in both are nouns.

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

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

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

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

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