(not in technical use) conjoined twin.
Origin of Siamese twin
First recorded in 1820–30; named after congenitally united twins, Chang and Eng (1811–74), born in Siam, who were joined to each other at the chest
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Medicine definitions for siamese twin
[ sī′ə-mēz′ ]
Either of a pair of conjoined twins. No longer in technical use.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.