Carbonated quaff
'carbonated quaff' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for soda that I've seen before include "for use with whisky?" , "Splash served with some spirits" , "Soft drink" , "Fizzy water, goes well with whiskey" , "Alkaline substance used in cleaning, drinks etc" .)
(Another definition for soda pop that I've seen is " Fizzy drink".)