a geological formation consisting of an underground enclosure with access from the surface of the ground or from the sea
source: WordNet 3.0
A hollow place in the earth, either natural or artificial; a subterraneous cavity; a cavern; a den.
source: Webster 1913
A coalition or group of seceders from a political party, as from the Liberal party in England in 1866. See Adullam, Cave of, in the Dictionary of Noted Names in Fiction.
