ph.

1. (屋顶、天花板等)塌陷，凹陷
If something such as a roof or a ceiling caves in, it collapses inwards.

2. (尤指迫于压力)突然停止争辩，让步，屈服
If you cave in, you suddenly stop arguing or resisting, especially when people put pressure on you to stop.

1. the sudden collapse of something into a hollow beneath it

Synonym: subsidence