Naked except for sweetheart (4)
I believe the answer is:
bare
'naked' is the definition.
('bare' can be a synonym of 'naked')
'except for sweetheart' is the wordplay.
'except' becomes 'bar' (**).
'for' says to put letters next to each other.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'bar'+'e'='BARE'
(Other definitions for bare that I've seen before include "Carried" , "Naked or empty" , "Unclad" , "State of deciduous tree in winter" , "Mere" .)