Siamese twins
Siamese twins were either of a pair of identical twins born with their bodies conjoined in some area.

In 2372, Captain Kathryn Janeway described the  and its duplicate as "Siamese twins linked at the ," upon learning that the ship's antimatter had not been duplicated and was tethering the two vessels. ()

See also
 "Joined at the hip"

External link 

de: Siamesische Zwillinge
Sex and reproduction
Slang
Medical conditions