Clown in ghastly supermarket (8)
I believe the answer is:
grimaldi
'clown' is the definition.
(I've seen this before)
'ghastly supermarket' is the wordplay.
'ghastly' becomes 'grim' (I've seen this in another clue).
'supermarket' becomes 'Aldi' (Aldi is a supermarket chain).
'grim'+'aldi'='GRIMALDI'
'in' is the link.
(Other definitions for grimaldi that I've seen before include "Ruling house of Monaco" , "Genoese family" , "Pantomime actor" , "Joseph -, eighteenth to nineteenth century English clown" , "English clown's" .)