A note to leave to friend (5)
I believe the answer is:
amigo
'friend' is the definition.
('friend' in Spanish)
'a note to leave' is the wordplay.
'note' becomes 'mi' (as in 'do re mi').
'to leave' becomes 'go'.
'a'+'mi'+'go'='AMIGO'
'to' is the link.
(Other definitions for amigo that I've seen before include "friend from Barcelona" , "Hispanic friend" , "Male (Spanish?) friend" , "friend in Uruguay" , "buddy abroad?" .)