Maintain a strong company (6)
I believe the answer is:
affirm
'maintain' is the definition.
(I've seen this before)
'a strong company' is the wordplay.
'strong' becomes 'f'.
'company' becomes 'firm' (I've seen this before).
'a'+'f'+'firm'='AFFIRM'
(Other definitions for affirm that I've seen before include "Maintain" , "Uphold" , "State as a fact, perhaps in court" , "Assert to be the case" , "Substantiate" .)