Note that's refreshing (5)
I believe the answer is:
tonic
This clue is a double definition.
'note' is the first definition.
(tonic is a kind of note)
'refreshing' is the second definition.
('tonic' can be a synonym of 'refreshing')
'that's' is the link.
(Other definitions for tonic that I've seen before include "Restorative that invigorates" , "Medical restorative" , "Key" , "Invigorating drink" , "Quinine water" .)