/ Dictionary / Index C castor-oil plant: Meaning and Definition of Find definitions for: cas'tor-oil' plant" Pronunciation: (kas'tur-oil', kä'stur-), [key] a tall plant, Ricinus communis, of the spurge family, cultivated for its ornamental foliage and having poisonous seeds that are the source of castor oil. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. castor oil castor sugar Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language