cave1
 
/
keɪv/
n.
 a large natural underground chamber.
v.
  - explore caves as a sport.
 - 
(cave in or US also cave)
 (of a roof or walls) subside or collapse.
 
Derivative
Etymology
ME: from OFr., from L. cava, from cavus ‘hollow’.
cave2
 
/
ˈkeɪvi/
exclam.
 Brit. school slang, dated look out!
Phrase
- keep cave
 act as lookout. 
Etymology
L., imper. of cavere ‘beware’.