Farm units (5)
'farm units' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for acres that I've seen before include "The Phoenix Park has 40 of them (5)" , "Areas of 4840 square yards" , "Scare (anag)" , "One of them has 4840 square yards" , "Cares about the tracts of land" .)
'farm units' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Another definition for bushels that I've seen is " Imperial capacity measures".)