natural enclosure

English Thesaurus

1. a naturally enclosed space (noun.object)

hypernym	:	space,
definition	:	an empty area (usually bounded in some way between things) (noun.shape)

hyponym	:	cavern,
definition	:	any large dark enclosed space (noun.object)

hyponym	:	matrix,
definition	:	an enclosure within which something originates or develops (from the Latin for womb) (noun.object)

derivation	:	confine, enclose, hold in,
definition	:	close in (verb.stative)

derivation	:	confine, enclose, hold in,
definition	:	close in (verb.stative)