Metric land measure (3)
I believe the answer is:
are
'metric land measure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for are that I've seen before include "is for more than one" , "(They/you/we) exist" , "Era (anag.)" , "Unit of land measure equal to 100 square metres" , "Is, in the plural" .)