See doctor about note on a beloved (4)
I believe the answer is:
dear
'beloved' is the definition.
(I know that beloved can be written as dear)
'see doctor about note on a' is the wordplay.
'see doctor' becomes 'd' (eg in PhD, Doctor of Philosophy).
'about' shows that the letters should be reversed in order.
'note' becomes 're' (as in do-re-mi).
'on' is an insertion indicator (as in clothing 'on' a person).
're' going around 'a' is 'rae'.
'rae' backwards is 'ear'.
'd'+'ear'='DEAR'
(Other definitions for dear that I've seen before include "Expensive -- honey" , "Beloved - expensive" , "love" , "letter opener" , "Beloved or costly" .)