Body's a ton, approximately (5)
I believe the answer is:
torso
'body's' is the definition.
('torso' can be a synonym of 'body')
'a ton approximately' is the wordplay.
'a ton' becomes 't' (**).
'approximately' becomes 'orso' ('or so' can be a synonym of 'approximately').
't'+'orso'='TORSO'
(Other definitions for torso that I've seen before include "Roost on trunk?" , "Main part of human body" , "Body, minus its head and limbs" , "Body without head, neck and limbs" , "Poorly-dressed child" .)