Old Greek character had to make good (7)
I believe the answer is:
expiate
'make good' is the definition.
(thesaurus)
'old greek character had' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'greek character' becomes 'pi' (letter from the Greek alphabet).
'had' becomes 'ate' (e.g. I had an ice cream).
'ex'+'pi'+'ate'='EXPIATE'
'to' is the link.
(Other definitions for expiate that I've seen before include "Pay for" , "right?" , "Atone for (guilt or wrongdoing)" , "Make up for mistake" , "Make amends for wrongdoing" .)