43rd US state (5)
I believe the answer is:
idaho
'43rd us state' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for idaho that I've seen before include "agricultural land" , "US state S. of Montana" , "My Own Private -- (1991 film)" , "The Gem State, known for its potatoes" , "One of 22 Across, capital Boise" .)