Firm hold file on origin of grievance (5)
I believe the answer is:
grasp
'firm hold' is the definition.
(thesaurus)
'file on origin of grievance' is the wordplay.
'file' becomes 'rasp' (rasp is a kind of file**).
'on' is a charade indicator (letters next to each other).
'origin of' suggests taking the first letters.
The initial letter of 'grievance' is 'g'.
'rasp' after 'g' is 'GRASP'.
(Other definitions for grasp that I've seen before include "Firmly grip" , "Understand; take in hand" , "Get hold of firmly" , "Hold tightly" , "Seize - comprehend" .)