Artist, one who imitates others (13)

I believe the answer is:

impressionist

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'artist' is the definition.
(I know that impressionist is a type of artist)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for impressionist that I've seen before include "Is he taking off" , "Mimic" , "one good at doing copies?" , "Person pretending to be another" , "artist?" .)

I've seen this clue in The Telegraph.

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