cave

Concise Oxford English Dictionary © 2008 Oxford University Press:
cave1 /keɪv/

▶noun a large natural underground chamber. ▶verb

• 1 explore caves as a sport.

• 2 (cave in or US also cave) (of a roof or walls) subside or collapse.

– derivatives
caver noun,
caving noun.

– origin ME: from OFr., from L. cava, from cavus ‘hollow’.

Concise Oxford English Dictionary © 2008 Oxford University Press:
cave2 /ˈkeɪvi/

▶exclamation Brit. school slang, dated look out!

– phrases
keep cave act as lookout.

– origin L., imper. of cavere ‘beware’.