Gram or gallon, for example (4)
I believe the answer is:
unit
I believe this clue is a double definition.
'gram' is the first definition.
(thesaurus)
'gallon for example' is the second definition.
(gallon is a kind of unit)
(Other definitions for unit that I've seen before include "Small military detachment" , "Piece of furniture" , "Entity, system; component group" , "Single person - group of people" , "Subdivision of a military group" .)