1 cavern, grotto, hollow, hole, cavity, den:
In the cave were prehistoric wall paintings.
2 cave in.
(a) collapse, break down, give way, subside, fall in or inwards:
The earthquake caused the walls of the house to cave in.
(b) yield, submit, give way; surrender; Colloq buckle, knuckle under:
After eight hours of questioning, he caved in and told them everything.