1. type of plant. ricinusrici*nus , n. [l., the castor-oil plant.] (bot.) a genus of plants of the spurge family, containing but one species (r. communis), the castor-oil plant. the fruit is three-celled, and contains three large seeds from which castor oil iss expressed. see: palma christi.ricinus a genus of herb having only one known species: castor-oil plant [syn: ricinus, genus ricinus]