Source : Webster's Revised Unabridged Dictionary (1913)

Catacomb \Cat"a*comb\, n. [It. catacomba, fr. L. catacumba perh.
   from Gr. kata` downward, down + ky`mbh cavity.]
   A cave, grotto, or subterraneous place of large extent used
   for the burial of the dead; -- commonly in the plural.

   Note: The terms is supposed to have been applied originally
         to the tombs under the church of St. Sebastian in Rome.
         The most celebrated catacombs are those near Rome, on
         the Appian Way, supposed to have been the place or
         refuge and interment of the early Christians; those of
         Egypt, extending for a wide distance in the vicinity of
         Cairo; and those of Paris, in abandoned stone quarries,
         excavated under a large portion of the city.

Source : WordNet®

catacomb
     n : an underground tunnel with recesses where bodies were buried
         (as in ancient Rome)