The one uncommonly concluded? (4)
I believe the answer is:
only
'the one' is the definition.
(thesaurus)
'uncommonly concluded?' is the wordplay.
'ONLY' is hidden within the letters.
But, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for only that I've seen before include "Existing alone with no other, perhaps a child" , "Simply" , "Solely, lone" , ". . . . the Lonely (sung by Roy Orbison)" , "Alone; solitary" .)