The most common and most likely answer to this crossword clue is the 9 letter word EXPERTISE
I've seen this crossword clue in The Daily Telegraph
E
X
P
E
R
T
I
S
E
More clues leading to the result EXPERTISE
- Duty that requires clubs to go for forward’s skill
- . Old forward is back in style, showing adroitness
- Understanding former wife, saucy one’s sweetheart
- Pet with sexier snaps showing professionalism
- Once impudent, is beginning to exercise savoir-faire
- Purge about giving way to brash punditry
- Former party leader reties knots — that’s skill
Buddy explains!

The straight part
We know that "Understanding" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case understanding = expertise.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 EXPERTISE mean?
EXPERTISE noun- Great skill or knowledge in a particular field or hobby.
- Advice, or opinion, of an expert.