Temperature, approximately, in part of body (5)
I believe the answer is:
torso
'part of body' is the definition.
('torso' is part of 'body')
'temperature approximately' is the wordplay.
'temperature' becomes 't' (abbreviation).
'approximately' becomes 'orso' ('or so' can be a synonym of 'approximately').
't'+'orso'='TORSO'
'in' is the link.
(Other definitions for torso that I've seen before include "Body, minus its head and limbs" , "Piece of bronze" , "Limbless statue" , "Body's core" , "Body without head, neck and limbs" .)