Painter entertained by diplomat is Seurat (7)
I believe the answer is:
matisse
'painter' is the definition.
(Henri Matisse, 1869-1954, French artist)
'entertained by diplomat is seurat' is the wordplay.
'entertained by' says the answer is hidden in the clue (the clue hosts or entertains the answer).
'MATISSE' is hidden within 'diplomat is seurat'.
(Other definitions for matisse that I've seen before include "20th century French painter" , "Henri ---, Fauvist painter" , "Henri -, Fr. artist" , "Leading fauvist painter, d. 1954" , "French painter, Henri, d.1954" .)