The Collaborative International Dictionary of English v.0.48:

Cereus \Ce"re*us\, n. [L., a wax candle, fr. cera wax. So named
   from the resemblance of one species to the columnar shape of
   a wax candle.] (Bot.)
   A genus of plants of the Cactus family. They are natives of
   America, from California to Chili.
   [1913 Webster]

   Note: Although several species flower in the night, the name
         Night-blooming cereus is specially applied to the
         Cereus grandiflorus, which is cultivated for its
         beautiful, shortlived flowers. The Cereus giganteus,
         whose columnar trunk is sometimes sixty feet in height,
         is a striking feature of the scenery of New Mexico,
         Texas, etc.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Cereus
    n 1: genus of much-branched treelike or shrubby cacti with
         pronounced ribs and rounded needlelike spines and nocturnal
         flowers usually white [syn: Cereus, genus Cereus]