The most common and most likely answer to this crossword clue is the 10 letter word STABLEMATE
I've seen this crossword clue in Independent
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More clues leading to the result STABLEMATE
- Fellow member, fit male, in condition
- Well-balanced wife maybe — or a nag?
- Draw includes black horse from same stud
- Colleague heading for breakdown in no-win situation?
- Impasse about black horse nearby?
- No-win situation involving black neighbour of Black Beauty?
- Opera singer’s comeback in New York, say, having the same trainer
- Colleague having tea with firm first
- Colleague heading for breakdown during deadlock
- Steady partner, one from the same place?
Buddy explains!

The straight part
We know that "horse nearby?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case horse nearby? = stablemate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does STABLEMATE mean?
STABLEMATE noun- One (such as a racehorse) from the same stable.
- One from the same organization or background.