I leave belligerent speech for business (5)
I believe the answer is:
trade
'for business' is the definition.
(trade is a kind of business)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for trade that I've seen before include "Commercial exchange of goods and services" , "Barter, do business" , "Rated (anag.)" , "Give and receive (blows)" , "Business - deal" .)