headmate

Etymology
. See.

Noun

 * 1) An imaginary friend.
 * 2) An alternate personality in someone with dissociative identity disorder or another form of psychological multiplicity.
 * 3) * 2018, "The Entropy System", Toi Magazine, December 2018/January 2019, page 56:
 * The first one of the headmates (our word for alter) I was aware of was a boy named Josh.
 * 1) * 2020, Tynan Drake, "Intersectional Representation: LGBTQ+ and neurodiverse voices in transmedia fiction", paper submitted to Ball State University, page 36:
 * With co-fronting, typically only one headmate at a time functions as the ‘main fronter’ who does the majority of physical driving of the body,

Usage notes

 * Not a medical term.