From The Collaborative International Dictionary of English v.0.48 :
Ricinus \Ric"i*nus\, n. [L., the castor-oil plant.] (Bot.)
A genus of plants of the Spurge family, containing but one
species ({Ricinus communis), the castor-oil plant. The fruit
is three-celled, and contains three large seeds from which
castor oil is expressed. See Palma Christi.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
Ricinus
n 1: a genus of herb having only one known species: castor-oil
plant [syn: Ricinus, genus Ricinus]