[Origin of name uncertain: it has been suggested that this oil actually took the place of the drug castor, or perh. of oil of castor (see CASTOR1 5), in use in midwifery, etc., and thus popularly assumed its name. So ‘Castor oil pills’ is now a popular name for certain pills that have the same laxative effect but contain no castor oil.]
A pale yellow oil obtained from the seeds of Ricinus communis or Palma Christi (N.O. Euphorbiaceæ), having a nauseous slightly acrid taste; used in medicine as a purgative, and in some parts of the world in lamps.
1746. P. Canvane (title), Dissertation on the Oleum Palmæ Christi … commonly called Castor Oil.
1799. Med. Jrnl., I. 468. A very useful medicine, where the stomach will bear it, is castor oil. Ibid. (1803), X. 492. His bowels to be kept open by castor oil.
1870. Yeats, Nat. Hist. Comm., 205. Castor-oil is obtained by expression from the seeds without heat, hence it is called ‘cold-drawn castor oil.’
fig. 1873. Tristram, Moab, xv. 28. The canebrake tops … are ‘castor-oil to camels’ stomachs.’
b. attrib., as in castor-oil plant or tree.
1845. Darwin, Voy. Nat., xxi. (1852), 492. An occasional green castor-oil plant … may be met with.
1857. Livingstone, Trav., xv. 272. The Palma-Christi, or castor-oil-plant.
