what is the name for a large molecule made up of many small units?

A large molecule made up of many small units is called a macromolecule. It is also commonly referred to as a polymer, especially when describing repeating subunits (monomers) linked together to form the long chain. Macromolecules include biological polymers like proteins, nucleic acids, and polysaccharides, as well as synthetic polymers such as plastics and fibers.