The most common and most likely answer to this crossword clue is the 8 letter word CENTAURS
I've seen this crossword clue in The Times
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More clues leading to the result CENTAURS
Buddy explains!
The straight part
We know that "race of “horsemen”" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case race of “horsemen” = centaurs.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 CENTAURS mean?
CENTAURS noun- A mythical beast having a horse's body with a man's head and torso in place of the head and neck of the horse.
- (also capitalised) An icy planetoid that orbits the Sun between Jupiter and Neptune.
- A chess-playing team comprising a human player and a computer who work together.