One who makes gift of two notes and eighteen letters (7)
I believe the answer is:
donator
'one who makes gift' is the definition.
(a donator gives)
'two notes and eighteen letters' is the wordplay.
'two notes' can mean two substitutions for 'note'.
'note' becomes 'do' (as in do-re-mi).
'note' becomes 'n' (abbreviation).
'and' is a charade indicator (letters next to each other).
'eighteen letters' becomes 'ator' (I can't justify this - if you can you should give a lot more credence to this answer).
'do'+'n'+'ator'='DONATOR'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for donator that I've seen before include "benefactor!" , "Someone giving" , "One will give" , "Giver" , "Presenter" .)