Fraction of a quart (4)
I believe the answer is:
pint
'fraction of a quart' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pint that I've seen before include "The working man's drink measure" , "Glass of beer (colloq.)" , "Unit of capacity" , "Standard measure of beer or milk" , "small amount" .)