Siamese twin
noun
(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
Medical definitions for siamese twin
Siamese twin
[ sī′ə-mēz′ ]
n.
Either of a pair of conjoined twins. No longer in technical use.