Sentence:  Their main asset is an abundance of unsaturated <WSD>fatty</WSD> acids , so necessary for maintaining the good health of the circulatory system . 
Meaning of the word marked with <WSD> tags:  any of a class of aliphatic monocarboxylic acids that form part of a lipid molecule and can be derived from fat by hydrolysis; fatty acids are simple molecules built around a series of carbon atoms linked together in a chain of 12 to 22 carbon atoms