early 13c., from Old French cave "a cave, vault, cellar" (12c.), from Latin cavea "hollow" (place), noun use of neuter plural of adjective cavus "hollow," from PIE root *keue- "a swelling, arch, cavity" (see cumulus). Replaced Old English eorðscrafu. First record of cave man is 1865.
early 15c., caven, "to hollow something out," from cave (n.). Modern sense "to collapse in or down" is 1707, American English, presumably from East Anglian dialectal calve "collapse, fall in," perhaps from Flemish; subsequently influenced by cave (n.). Transitive sense by 1762. Related: Caved; caving. Figurative sense of "yield to pressure" is from 1837.
A naturally occurring underground hollow or passage, especially one with an opening to the surface of the Earth. Caves can form through a variety of processes, including the dissolution of limestone by flowing water, the differential cooling of volcanic magma (which occurs when the outside surface of the lava cools, but the inside continues to flow downwards, forming a hollow tube), or the action of wind and waves along a rocky coast.