Farmland units (5)
I believe the answer is:
acres
'farmland units' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for acres that I've seen before include "Scare (anag)" , "Units of area" , "Cares about the land measures" , "Cares about the tracts of land" , "One of them has 4840 square yards" .)