Dark beer
'dark beer' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stout that I've seen before include "Bulky" , "Dark beer; of heavy build" , "Full-bodied" , "Kind of beer" , "Thick; beer" .)
(Other definitions for brown ale that I've seen before include "Dark, mild beer" , "bottled beer" , "Dark, malty beer" , "Noble war (anag) - drink" , "Type of beer" .)