Something added to drink, note (5)
I believe the answer is:
tonic
'note' is the definition.
(type of note in a musical scale)
'something added to drink' is the wordplay.
I cannot quite understand how this works, but
'to' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tonic that I've seen before include "Restorative that invigorates" , "Quinine drink; keynote" , "It goes with gin" , "Fillip" , "something invigorating" .)