Catacombs: word definition

Catacomb, Latin CATACUMBA, Italian CATACOMBA, subterranean cemetery composed of galleries or passages with side recesses for tombs. The term, of unknown origin, seems to have been applied first to the subterranean cemetery under the Basilica of San Sebastiano (located on the Appian Way near Rome), which was reputed to have been the temporary resting place of the bodies of Saints Peter and Paul in the last half of the 3rd century. By extension, the word eventually came to refer to subterranean cemeteries.

Encyclopaedia Britannica, 1994