The most common and most likely answer to this crossword clue is the 8 letter word CARACOLE
C
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The straight part
We know that "half-turn" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case half-turn = caracole.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 CARACOLE mean?
CARACOLE noun- A half-turn performed by a horse and rider in dressage.
- (cavalry) A combat maneuver where riders of the same squadron turn simultaneously to their left or to their right.
- A spiral staircase.
- To execute a caracole.