Body temperature, approximately (5)
I believe the answer is:
torso
'body' is the definition.
(a person's middle)
'temperature approximately' is the wordplay.
'temperature' becomes 't' (abbreviation).
'approximately' becomes 'or so' (synonyms).
't'+'orso'='TORSO'
(Other definitions for torso that I've seen before include "part of body will be found" , "Trunk; headless, limbless body" , "Trunk of human body" , "Body, minus its head and limbs" , "Trunk, something unfinished" .)