Two bodies that are combined but retain their individual identities

Am unable to recall (stroke with memory issues) a word that starts with x (if I even recall that correctly) that defines two bodies (or people or entities) that are bonded but retain their individual identities.

Conjoined as in conjoined twins, who are connected but two people.

Does not begin with “X” though.

Looking through Chambers on my phone for words beginning with x (and also here),

xenomorphic

is the nearest I can find:

“A textual term applied to rock minerals which do not show their original shape”

But the sense would seem to be the opposite of that stated in the question. I wonder whether the poster has misremembered this.