The most common and most likely answer to this crossword clue is the 13 letter word IMPRESSIONIST
I've seen this crossword clue in The Daily Telegraph
I
M
P
R
E
S
S
I
O
N
I
S
T
More clues leading to the result IMPRESSIONIST
- One copies Manet for instance
- One to copy Renoir, say
- Is he taking off as an artist?
- One churning out some prints is artist
- Artist who copies Monet among others?
- Painter, I rework Monet’s ‘Irises’, power replacing energy
- One takes off in turn
- Painter or Dentist?
- Artist, demon with racket, endlessly going back into combat
Buddy explains!

The straight part
We know that "Painter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case painter = impressionist.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 IMPRESSIONIST mean?
IMPRESSIONIST noun- One who adheres to the theory or method of impressionism.