Huge figure of Russian writer seizing doughnut (6)
I believe the answer is:
googol
'huge figure' is the definition.
(a googol is 10 to the power of 100)
'russian writer seizing doughnut' is the wordplay.
'russian writer' becomes 'gogol' (novelist Nikolai Gogol).
'seizing' indicates putting letters inside.
'doughnut' becomes 'o' (letter resembling a doughnut).
'gogol' enclosing 'o' is 'GOOGOL'.
'of' acts as a link.
(Other definitions for googol that I've seen before include "Vast figure" , "Big number" , "Ten to the power of 100" , "very large number" , "extraordinary figure" .)