Greek character thus in harmony (5)
I believe the answer is:
music
'harmony' is the definition.
(thesaurus)
'greek character thus' is the wordplay.
'greek character' becomes 'mu' (letter from the Greek alphabet).
'thus' becomes 'sic' ('sic' can be a synonym of 'thus').
'mu'+'sic'='MUSIC'
'in' is the link.
(Other definitions for music that I've seen before include "Harmonious sound (generally!)" , "orchestral work" , "Harmonious sounds" , "(Pleasant) sequence of sounds" , "Shakespeare: 'If . . . . . be the food of love, play on'" .)