Answer is: addition.
This is example of polymerization (addition of monomers to form polymer).
For example, plastic is organic polymers of high molecular mass derived from petrochemicals.
Another example, starch (carbohydrate) is a polymeric carbohydrate consisting of a large number of glucose units (monomers) bonded by glycosidic bond.
Polystyrene is a synthetic aromatic hydrocarbon polymer made from the monomer styrene.
