A low-molecular-weight compound that can be reacted and united with other low-molecular-weight compounds to form a long, higher-molecular-weight chain-like polymer. The formation of polymers—a chemical process called polymerization—is the basis of the drying of many types of printing inks, commonly preceded by the chemical process of oxidation, and many printing ink resins are produced by the process of polymerization. A monomer is considered the basic structural unit of a polymer, and various smaller combinations of monomers are described as dimers, trimers, or oligomers.