Firm with bully (3)
I believe the answer is:
cow
'bully' is the definition.
(cow can mean to bully or oppress)
'firm with' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'with' becomes 'w' (abbreviation).
'co'+'w'='COW'
(Other definitions for cow that I've seen before include "Subdue with threats or force" , "female whose homecoming is indefinitely delayed" , "Frighten with intimidations" , "frighten as with threats" , "Subdue the spirit" .)