The most common and most likely answer to this crossword clue is the 3 plus 2 plus 5 letter word NIL BY MOUTH
I've seen this crossword clue in The Guardian
N
I
L
B
Y
M
O
U
T
H
More clues leading to the result NIL BY MOUTH
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.