Canters off with North Dakota specialist; Athol ends superior (14)
I believe the answer is:
transcendental
'superior' is the definition.
(thesaurus)
'canters off with north dakota specialist athol ends' is the wordplay.
'off' indicates anagramming the letters.
'with' means one lot of letters go next to another.
'north dakota' becomes 'ND' (abbreviation for the US state).
'specialist' becomes 'ent' (Ear, Nose and Throat specialist).
'ends' means to remove the middle letters.
'athol' with its centre removed is 'al'.
'canters' with letters rearranged gives 'transce'.
'transce'+'nd'+'ent'+'al'='TRANSCENDENTAL'
(Other definitions for transcendental that I've seen before include "'being in the spiritual realms' maybe" , "Supereminent" , "Relating to the spiritual realm" , "Pi is" , "like a number of mathematicians?" .)