The most common and most likely answer to this crossword clue is the 5 letter word FLEER
F
L
E
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R
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The straight part
We know that "One escaping/mockery" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one escaping/mockery = fleer.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 FLEER mean?
FLEER noun- Mockery; derision
- To make a wry face in contempt, or to grin in scorn
- To grin with an air of civility; to leer.
- One who flees