Measure enclosed area (4)
I believe the answer is:
yard
I believe this clue is a double definition.
'measure' is the first definition.
(yard is a kind of measure)
'enclosed area' is the second definition.
(I've seen this before)
(Other definitions for yard that I've seen before include "36 inches" , "short distance" , "area behind the house" , "Linear measure" , "Unit of distance" .)