the Diamond State (8)
I believe the answer is:
delaware
'the diamond state' is the definition.
('Delaware' can be a synonym of 'diamond state')
This is all the clue.
(Other definitions for delaware that I've seen before include "Second smallest US state" , "Atlantic state of the US" , "The Diamond State, capital Dover" , "Small E. coast US state" , "state of the east" .)