An unsaturated fatty acid with one double bond, CH3(CH2)7CH=CH(CH2)7COOH; r.d. 0.9; m.p. 13°C. Oleic acid is one of the most abundant constituent fatty acids of animal and plant fats, occurring in butterfat, lard, tallow, groundnut oil, soya-bean oil, etc. Its systematic chemical name is cis-octadec-9-enoic acid.