The most common and most likely answer to this crossword clue is the 2 plus 5 plus 3 plus 4 plus 2 plus 4 letter word TO THINE OWN SELF BE TRUE
I've seen this crossword clue in Independent
T
O
T
H
I
N
E
O
W
N
S
E
L
F
B
E
T
R
U
E
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.