The most common and most likely answer to this crossword clue is the 7 letter word PIANIST
I've seen this crossword clue in The Times
P
I
A
N
I
S
T
More clues leading to the result PIANIST
- Perfectionist maybe disposing of uranium to key operator
- Key expert's hint about wrong answer completely rejected
- In place of orchestra, is after a new musician
- ‘Thespian’ is term that describes Victoria Wood, perhaps
- . A name is inscribed in orchestra area identifying instrumentalist
- Unfinished track cut by a popular backing musician …
- Spiritual number is put in hands of six-footer as source of music
- Monk perhaps is obstructing devout worker
- Player: one is found in orchestral area
- Man is put into part — player on stage?
Buddy explains!

The straight part
We know that "Key expert" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case key expert = pianist.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 PIANIST mean?
PIANIST noun- A person who plays the piano, particularly with skill or as part of an orchestra.
- (WWII) A spy using radio or wireless telegraphy to keep in touch with headquarters during the Second World War