The most common and most likely answer to this crossword clue is the 11 letter word PORTRAITIST
P
O
R
T
R
A
I
T
I
S
T
More clues leading to the result PORTRAITIST
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 = portraitist.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.
Crossword Answer definitions
PORTRAITIST noun- A painter or photographer who makes portraits.