The most common and most likely answer to this crossword clue is the 4 plus 2 letter word SHUT UP
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More clues leading to the result SHUT UP
Buddy explains!
The straight part
We know that "Keep mum" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case keep mum = shut up.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 SHUT UP mean?
SHUT UP adjective- Closed up or off, as in a building that no one is to enter.