A macromolecule that has one end-group which enables it to act as a monomer molecule, contributing only a single monomeric unit to a chain of the final macromolecule.
Source:
PAC, 1996, 68, 2287. 'Glossary of basic terms in polymer science (IUPAC Recommendations 1996)' on page 2290 (https://doi.org/10.1351/pac199668122287)