IPA: //ˈsteɪbəlˌmeɪt//
KK: /ˈsteɪbəlˌmeɪt/
A person or animal that comes from the same place or organization as another, often used to refer to racehorses that are kept in the same stable.
The two racehorses were stablemates, training together every day.
Stablemate is formed from "stable" (from Old French *estable*, meaning firm or fixed) and "mate" (from Old English *gemetta*, meaning companion or associate). The word refers to a companion or associate that is found in the same stable, often used in the context of horses.
Think of a 'stable' where horses are kept and a 'mate' as a companion — a stablemate is simply a companion found in the same stable.