The most common and most likely answer to this crossword clue is the 8 letter word PIAFFING
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The straight part
We know that "moving on the spot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moving on the spot = piaffing.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 PIAFFING mean?
PIAFFING verb- To strut pretentiously, to parade about.
- To trot a horse with a high, slow, step, lifting the feet but without moving forward significantly.
- To ride a horse in this way.