Merriam-Webster Collegiate Dictionary - fatty acid

 noun  Date: 1838  1. any of numerous saturated aliphatic monocarboxylic acids CnH2n+1COOH (as acetic acid) including many that occur naturally usually in the form of esters in fats, waxes, and essential oils  2. any of the saturated or unsaturated monocarboxylic acids (as palmitic acid) usually with an even number of carbon atoms that occur naturally in the form of glycerides in fats and fatty oils