Source : WordNet®

cave in
     n : the sudden collapse of something into a hollow beneath it
         [syn: {subsidence}]
     v : 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" [syn: {collapse},
          {fall in}, {give}, {give way}, {break}, {founder}]