The most common and most likely answer to this crossword clue is the 4 letter word PENT
I've seen this crossword clue in Financial Times
P
E
N
T
More clues leading to the result PENT
Buddy explains!
The straight part
We know that "Shut up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shut up = pent.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 PENT mean?
PENT verb- To enclose in a pen.
- Confinement; concealment.
- Confined in a pen, imprisoned.
- A pentatonic scale.
- A pentacle or pentagram.