Improves the definition of (5)
I believe the answer is:
tones
'improves the definition of' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tones that I've seen before include "Qualities of people's voices" , "Told about the silly ass" , "Tints of colour" , "Notes, characters" , "Shades" .)