Start to enjoy the old organ (3)
I believe the answer is:
eye
'organ' is the definition.
(eye is a kind of organ)
'start to enjoy the old' is the wordplay.
'start to' says to take the initial letters.
'the old' becomes 'ye'.
The initial letter of 'enjoy' is 'e'.
'e'+'ye'='EYE'
(Other definitions for eye that I've seen before include "Optical organ" , "Regard" , "Good discernment" , "Ireland's . . ., off the Dublin coast" , "Observe narrowly" .)