A dimer's a chemical or biological entity consisting of two structurally similar subunits called monomers, which are held together by either intramolecular forces (covalent bonds) or weaker intermolecular forces. Chemistry An example of a molecular dimer (for example held together by intramolecular forces)'s dicyclopentadiene, wherein two cyclopentadiene molecules have reacted to give the product. Molecular dimers are often formed by the reaction of two identical compounds for example: 2A … (More on Dimer)