The most common and most likely answer to this crossword clue is the 5 letter word DEMON
I've seen this crossword clue in The Times
D
E
M
O
N
More clues leading to the result DEMON
- Ace performer’s way of working in study
- Excellent protest at noon
- Doctor in private room, a person of great energy
- Monster public protest before noon
- Spirit shown in March and November
- Devil’s lair imprisoning little Maureen
- Bad spirit of public protest over conclusion of coalition
- Devil in protest over the ending of sin
- March the first in Newtown is ace!
- I show spirit how to work in office
Buddy explains!

The straight part
We know that "Ace performer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ace performer = demon.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 DEMON mean?
DEMON noun- An evil supernatural spirit.
- A neutral supernatural spirit.
- Someone with great strength, passion or skill for a particular activity, pursuit etc.; an enthusiast.
- A form of patience (known as Canfield in the US).
- Any of various hesperiid butterflies of the genera Notocrypta and Udaspes.