The Collaborative International Dictionary of English v.0.48:

Rhus \Rhus\, n. [L., sumac, fr. Gr. ???.] (Bot.)
   A genus of shrubs and small treets. See Sumac.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Rhus
    n 1: deciduous or evergreen shrubs and shrubby trees of
         temperate and subtropical North America, South Africa,
         eastern Asia and northeastern Australia; usually limited to
         nonpoisonous sumacs (see genus Toxicodendron) [syn: Rhus,
         genus Rhus]