Yes: sounding like organ (3)
I believe the answer is:
aye
'yes' is the definition.
(thesaurus)
'sounding like organ' is the wordplay.
'sounding like' shows a homophone (sound like).
'organ' becomes 'eye' (eye is a kind of organ).
'eye' is a homophone of 'AYE'.
(Other definitions for aye that I've seen before include "Yes vote" , "Entirely one" , "Always" , "Affirmative answer" , "Indeed" .)