The most common and most likely answer to this crossword clue is the 9 letter word EXCELLENT
I've seen this crossword clue in The Daily Telegraph
E
X
C
E
L
L
E
N
T
More clues leading to the result EXCELLENT
- Extremely good for former partner to find a girl in Connecticut
- Office data analyser that’s fast is superb
- Spreadsheet program “fast”, “brilliant”
- Outdo others with a fast time – fantastic!
- Superb spreadsheet provided for limited time?
- Former prison abutting part of hospital in capital
- No longer having little room, hospital department is first-class
- Select former unit on hospital department
- First-class old mini-dwelling ending with the National Trust
- Sailing dame going after former partner in court knockout
Buddy explains!

The straight part
We know that "first-class" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case first-class = excellent.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 EXCELLENT mean?
EXCELLENT adjective- Having excelled, having surpassed.
- Of higher or the highest quality; splendid.
- Exceptionally good of its kind.
- Superior in kind or degree, irrespective of moral quality.
- Excellently.