The Collaborative International Dictionary of English v.0.48:

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.
       [1913 Webster]