The most common and most likely answer to this crossword clue is the 2 plus 4 plus 9 letter word IN FULL AGREEMENT
I
N
F
U
L
L
A
G
R
E
E
M
E
N
T
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.