The most common and most likely answer to this crossword clue is the 12 letter word INCOMPARABLE
I've seen this crossword clue in The Daily Telegraph
I
N
C
O
M
P
A
R
A
B
L
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.
What does INCOMPARABLE mean?
INCOMPARABLE noun- Something beyond compare; a thing with which there is no comparison.
- So much better than another as to be beyond comparison; matchless or unsurpassed.
- Not able to be compared.