This improved with right top (5)
I believe the answer is:
shirt
'top' is the definition.
(I've seen this in another clue)
'this improved with right' is the wordplay.
'improved with' is an anagram indicator.
'right' becomes 'r' (common abbreviation).
'this' anagrammed with 'r' can make 'SHIRT'.
(Other definitions for shirt that I've seen before include "Man's garment" , "One may lose it at the bookie's" , "Garment for upper male body, usually cotton" , "Male garment worn with tie" , "tailored garment" .)