A uniform state (4)
I believe the answer is:
peru
'state' is the definition.
(Peru is an example)
'a uniform' is the wordplay.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'per'+'u'='PERU'
(Other definitions for peru that I've seen before include "Mario Vargas Llosa's native land" , "Machu Picchu country" , "Paddington Bear's country of birth" , "South American republic" , "Lima's country" .)