Daughter on organ, expensive (4)
I believe the answer is:
dear
'expensive' is the definition.
(I've seen this before)
'daughter on organ' is the wordplay.
'daughter' becomes 'd'.
'on' says to put letters next to each other.
'organ' becomes 'ear' (ear is a kind of organ).
'd'+'ear'='DEAR'
(Other definitions for dear that I've seen before include "letter opener" , "Beloved - expensive" , "Overpriced" , "Precious" , "Beloved or costly" .)