a colorless or yellowish oil from castor beans, used as a cathartic, lubricant, etc.
See castor oil in American Heritage Dictionary 4
noun
A colorless or pale yellowish oil extracted from the seeds of the castor-oil plant, used pharmaceutically as a laxative and skin softener and industrially as a lubricant.
Origin:
Origin: Possibly from a former use as a substitute for castor in medicine