The most common and most likely answer to this crossword clue is the 4 letter word CLOP
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The straight part
We know that "Sound made by coach and horse" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sound made by coach and horse = clop.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 CLOP mean?
CLOP noun- The sound of a horse's shod hoof striking the ground.
- My Little Pony-themed pornography
- To make this sound; to walk so as to make this sound.