Originally: the castor oil plant, Ricinus communis, a shrub native to the Mediterranean, eastern Africa, and parts of Asia and naturalized throughout the tropics, having alternate palmate leaves and seeds which are the source of castor oil and of the toxic substance ricin. In later use also (in form Ricinus): the genus of the family Euphorbiaceae to which this plant belongs.
Old English; earliest use found in Pseudo-Apuleius' Herbarium. From classical Latin ricinus castor oil plant (Pliny), of unknown origin.
A tick; especially the dog tick, Ixodes ricinus.
Mid 17th century; earliest use found in John Rowland (fl. c1658). From classical Latin ricinus parasite on sheep or other animals, tick, of unknown origin; perhaps the same word as classical Latin ricinus. Adopted in scientific Latin as ricinus, specific name (in Acarus ricinus, LinnaeusSystema naturae (ed. 10, 1758) I. 615).