Macromolecule. Definition. noun, plural: macromolecules. A large complex molecule, such as nucleic acids, proteins, carbohydrates, and lipids, with relatively large molecular weight.Supplement. In biology, a macromolecule is a term used to contrast a micromolecule (which is smaller in size and in molecular weight).Macromolecules are usually used to refer to large biological polymers, such as nucleic acids and proteins, which are made up of small monomers linked together.upplement. In biology, a macromolecule is a term used to contrast a micromolecule (which is smaller in size and in molecular weight). Macromolecules are usually used to refer to large biological polymers, such as nucleic acids and proteins, which are made up of small monomers linked together.