The most common and most likely answer to this crossword clue is the 7 letter word JAYWALK
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The straight part
We know that "Don’t use 25" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case don’t use 25 = jaywalk.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 JAYWALK mean?
JAYWALK verb- To behave as a jaywalker; to violate pedestrian traffic regulations by crossing a street away from a designated crossing or to walk in the part of the street intended for vehicles rather than on the sidewalk.