The most common and most likely answer to this crossword clue is the 10 letter word COARSENING
I've seen this crossword clue in The Daily Telegraph
C
O
A
R
S
E
N
I
N
G
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 COARSENING mean?
COARSENING verb- To make (more) coarse.
- To become (more) coarse.