Source : Webster's Revised Unabridged Dictionary (1913)

Columbarium \Col`um*ba"ri*um\, n.; pl. L. {Columbaria} [L. See
   {Columbary}.] (Rom. Antiq.)
   (a) A dovecote or pigeon house.
   (b) A sepulchral chamber with niches for holding cinerary
       urns.

Source : WordNet®

columbarium
     n 1: a niche for a funeral urn containing the ashes of the
          cremated dead [syn: {cinerarium}]
     2: a sepulchral vault or other structure having recesses in the
        walls to receive cinerary urns
     [also: {columbaria} (pl)]