The Bluegrass State? (8)
I believe the answer is:
kentucky
'the bluegrass state' is the definition.
('Kentucky' can be a synonym of 'bluegrass state')
This is the entire clue.
(Other definitions for kentucky that I've seen before include "American state" , "US Bluegrass State" , "US state with an annual Derby race since 1875" , "Derby area" , "Producer of Bourbon" .)