Initials of Giotto on drawings seen in gallery (4)
I believe the answer is:
gods
'gallery' is the definition.
(I've seen this in other clues)
'initials of giotto on drawings seen' is the wordplay.
'initials of' suggests taking the first letters.
The initial letters of 'giotto on drawings seen' is 'GODS'.
'in' is the link.
(Other definitions for gods that I've seen before include "Superhuman beings" , "objects of worship" , "Area of theatre" , "Supernatural beings" , "Gallery of a theatre" .)