Eighth of a gallon (4)
I believe the answer is:
pint
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">eighth of a gallon</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for pint that I've seen before include "Measure of the plain man's alcoholic drink" , "Liquid measure" , "The working man's beer measure" , "Unit of capacity" , "One eighth of a gallon" .)