Potter, say, in part, is a necromancer (7)
I believe the answer is:
artisan
'potter say' is the definition.
(potter is a kind of artisan)
'in part is a necromancer' is the wordplay.
'in' indicates a hidden word.
'ARTISAN' is hidden within 'part is a necromancer'.
(Other definitions for artisan that I've seen before include "Tsarina (anag.)" , "Train as (anag) - craftsman" , "man with skill" , "Skilled worker at craft or trade" , "craftsman of his trade" .)