The shape of accountant shot in study (7)
I believe the answer is:
decagon
'the shape' is the definition.
(decagon is a kind of shape)
'accountant shot in study' is the wordplay.
'accountant' becomes 'ca' (abbreviation for chartered accountant).
'shot' becomes 'go' (I've seen this in other clues**).
'in' is an insertion indicator.
'study' becomes 'den' (I've seen this before).
'ca'+'go'='cago'
'cago' put within 'den' is 'DECAGON'.
'of' acts as a link.
(Other definitions for decagon that I've seen before include "A polygon -- eg can-do (anag)" , "Go, dance on geometric figure with ten sides" , "Figure with 10 sides" , "10-sided figure" , "Ten-sided shape" .)