cave in is a noun and verb meaning "the sudden collapse of something into a hollow beneath it". It carries 2 recorded senses.
the sudden collapse of something into a hollow beneath it
break down, literally or metaphorically
“The wall collapsed”
“The business collapsed”
“The dam broke”
“The roof collapsed”
“The wall gave in”
“The roof finally gave under the weight of the ice”
Definitions, synonyms and semantic relations for cave in come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.