(momer.) A molecule or compound, usually containing carbon and of relatively low molecular weight and simple structure, that is capable of conversion to polymers, synthetic resins, or elastomers by combination with itself or other similar molecules or compounds. Thus, styrene is the monomer from which polystyrene resins are produced and vinyl chloride is the monomer of polyvinyl chloride. Other common monomers are methyl methacrylate, adipic acid, and hexamethylenediamine.