A little of a lot?
I believe the answer is:
'a little of a lot?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for acre that I've seen before include "Old unit of area - old port" , "in Western Brazil" , "4840 sq yds" , "marine location in Israel" , "Unit of area of 4,840 square yards" .)