A mug's drink, largely? (4)
I believe the answer is:
pint
'a mug's' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe there's a link between them I don't understand?
'drink largely?' is the wordplay.
'drink' becomes 'pinta' (I've seen this before).
'largely?' means to remove the last letter (most but not all of the letters).
'pinta' with its last letter taken off is 'PINT'.
Can you help me to learn more?
(Other definitions for pint that I've seen before include "Standard measure of Guinness" , "Quantity" , "small amount" , "Unit of beer" , "Standard measure of beer or milk" .)