stablemate

[ stey-buh l-meyt ]
/ ˈsteɪ bəlˌmeɪt /

noun

a horse sharing a stable with another.
one of several horses owned by the same person.
Informal. a person or thing originating from or belonging to the same establishment, field, etc., as another.

Origin of stablemate

First recorded in 1925–30; stable1 + mate1