The Collaborative International Dictionary of English v.0.48:

Suwarrow \Su*war"row\, n. (Bot.)
   The giant cactus (Cereus giganteus); -- so named by the
   Indians of Arizona. Called also saguaro.
   [1913 Webster]

WordNet (r) 3.0 (2006):

saguaro
    n 1: extremely large treelike cactus of desert regions of
         southwestern United States having a thick columnar sparsely
         branched trunk bearing white flowers and edible red pulpy
         fruit [syn: saguaro, sahuaro, Carnegiea gigantea]