Model or begin to sculpt round trunk (5)
I believe the answer is:
torso
'trunk' is the definition.
(synonyms)
'model or begin to sculpt round' is the wordplay.
'model' becomes 't' (Ford Model T car).
'begin to' suggests taking the first letters (I've seen 'beginning to' mean this).
'round' becomes 'o' (round can mean a round object).
The first letter of 'sculpt' is 's'.
't'+'or'+'s'+'o'='TORSO'
(Other definitions for torso that I've seen before include "Roost (anag)" , "Body's trunk" , "upper body" , "Roots out in trunk of the body" , "Main part of human body" .)