The most common and most likely answer to this crossword clue is the 5 letter word MOUSY
I've seen this crossword clue in Financial Times
M
O
U
S
Y
Buddy explains!

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 MOUSY mean?
MOUSY noun- A mouse.
- Resembling a mouse.
- Abounding or infested with mice.