1) Equus caballus 2) Horse 3) Level-headed groom 4) One to horse around with 5) Stable companion 6) Steadfast spouse 
[n] - a horse stabled with another or one of several horses owned by the same person
stable companion noun a horse stabled with another or one of several horses owned by the same person
a horse sharing a stable with another. · one of several horses owned by the same person. · a person or thing originating from or belonging to the same establishment, field, etc., as another.
Fighters who train at the same gym or under the banner of the same promoter.
When two fighters train in the same gym, fight for the same manager or promoter, they are oftentimes called stablemates.