All good, by the sound of it (6)
I believe the answer is:
wholly
'all' is the definition.
(synonyms)
'good by the sound of it' is the wordplay.
'good' becomes 'holy'.
'by the sound of it' shows a homophone (sound like).
'holy' is a homophone of 'WHOLLY'.
(Other definitions for wholly that I've seen before include "Totally" , "Altogether" , "in every respect" , "One hundred per cent" , "Entirely, fully" .)