Small part of French operation (8)
I believe the answer is:
'small part' is the definition.
(I've seen this before)
'french operation' is the wordplay.
'french' becomes 'fr' (abbreviation).
'operation' becomes 'action'.
'of' is the link.
(Other definitions for fraction that I've seen before include "Proportional" , "Small piece forming part of a whole" , "Small proportion" , "little bit" , "Number of mathematicians" .)