Trunk initially treated roughly (5)
I believe the answer is:
torso
'trunk' is the definition.
('torso' can be a synonym of 'trunk')
'initially treated roughly' is the wordplay.
'initially' says to take the initial letters.
'roughly' becomes 'orso' ('or so' can be a synonym of 'roughly').
The initial letter of 'treated' is 't'.
't'+'orso'='TORSO'
(Other definitions for torso that I've seen before include "Trunk; headless, limbless body" , "Trunk of human body" , "upper body" , "Body without head, neck and limbs" , "Body's trunk" .)