The number of central atoms joined in a single coordination entity by bridging ligands or metal-metal bonds is indicated by dinuclear, trinuclear, tetranuclear, polynuclear, etc.
Source:
PAC, 1997, 69, 1251. 'Glossary of terms used in bioinorganic chemistry (IUPAC Recommendations 1997)' on page 1288 (https://doi.org/10.1351/pac199769061251)