Ratify a fine company (6)
I believe the answer is:
affirm
'ratify' is the definition.
(I've seen this before)
'a fine company' is the wordplay.
'a fine' becomes 'af' (I've seen this in other clues).
'company' becomes 'firm' (I've seen this before).
'af'+'firm'='AFFIRM'
(Other definitions for affirm that I've seen before include "Assert, avow" , "Declare, assert" , "Avow or corroborate" , "Maintain" , "Make a formal declaration (rather than an oath)" .)