Source : Webster's Revised Unabridged Dictionary (1913)

Impressionist \Im*pres"sion*ist\, n. [F. impressionniste.] (Fine
   Arts)
   One who adheres to the theory or method of impressionism, so
   called.

Source : WordNet®

impressionist
     adj : relating to or characteristic of impressionism;
           "impressionist music" [syn: {impressionistic}]

impressionist
     n : a painter who follows the theories of impressionism