The Collaborative International Dictionary of English v.0.48:

Salix \Sa"lix\, n.; pl. Salices. [L., the willow.] (Bot.)
   (a) A genus of trees or shrubs including the willow, osier,
       and the like, growing usually in wet grounds.
   (b) A tree or shrub of any kind of willow.
       [1913 Webster]

WordNet (r) 3.0 (2006):

Salix
    n 1: a large and widespread genus varying in size from small
         shrubs to large trees: willows [syn: Salix, genus
         Salix]