fatty acid: 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
opsonin: an antibody in blood serum that attaches to invading microorganisms and other antigens to make them more susceptible to the action of phagocytes