Measure - could be a yard (4)
I believe the answer is:
area
I believe this clue is a triple definition!
'measure' is the first definition.
(thesaurus)
'could' is a link.
'be a' is the second definition.
(maths abbreviation)
'yard' is the third definition.
(thesaurus)
(Other definitions for area that I've seen before include "Patch" , "field of study" , "Part of a building, city etc" , "Length multiplied by breadth" , "Geographical region" .)