What could be pints of tonic (7)
I believe the answer is:
bitters
'tonic' is the definition.
The definition and answer can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for bitters that I've seen before include "Angostura - - , a cocktail flavouring" , "Flavoured alcoholic liquor" , "Sharp-tasting additive" , "Traditional beers" .)