One (such as a racehorse) from the same stable.(noun)
One from the same organization or background.(noun)
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Use "stablemate" in a sentence
"The Daily Mirror and the Racing Post are no longer part of the same newspaper group, so any accusations that I'm toadying to the bosses of a stablemate are a long way wide of the mark."
"GH: Finally, does Dacha have much interaction with its "stablemate""
"Against George Groves, his detested former stablemate, DeGale has a blemish to rectify."