One of a pair of identical twins fused together with varying degrees of union and of residual duplication of organs.
See also: parasitic twin
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 739 (https://doi.org/10.1515/pac-2015-1202)