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Webster 1913 Edition

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Noun.

;

pl.

Hypogea

(#)

[L., fr. Gr. [GREEK], [GREEK], subterranean; [GREEK] under + [GREEK], [GREEK], the earth.]

(Anc. Arch.)

The subterraneous portion of a building, as in amphitheaters, for the service of the games; also, subterranean galleries, as the catacombs.

Noun.

[Gr. under, and the earth.] A name given by ancient architects to all the parts of a building which were under ground, as the cellar, &c.

hypogeum ‎(plural hypogeums or hypogea)

An underground room or cavern (also used figuratively).
- 1969, JG Ballard, The Atrocity Exhibition:
  Contour: the unique parameters of Karen’s body – beckoning vents of mouth and ****, the soft hypogeum of the anus.

underground vault