Invigorating drink (5)
I believe the answer is:
tonic
'invigorating drink' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tonic that I've seen before include "makes you feel good?" , "requirement for invigoration?" , "Fillip" , "Quinine drink; keynote" , "that may be mixed with gin" .)