Salutation in an old-fashioned love letter (7)
I believe the answer is:
dearest
'salutation in an old-fashioned love letter' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dearest that I've seen before include "The beloved one is most costly" , "Loved one" , "most delightful" , "Most precious or expensive" , "Darling" .)