syncytium (n.), syncytial (adj.)

https://doi.org/10.1351/goldbook.11275
Referring to a large multinucleated mass of cellular contents that arises from the fusion of originally individual cells.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 810 (https://doi.org/10.1515/pac-2015-1202)