The most common and most likely answer to this crossword clue is the 12 letter word TIGHT-LIPPED
I've seen this crossword clue in Financial Times
T
I
G
H
T
-
L
I
P
P
E
D
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 TIGHT-LIPPED mean?
TIGHT-LIPPED adjective- Having the lips pressed together.
- Unwilling to divulge information.