Discerning but terribly pious caprices (13)
I believe the answer is:
perspicacious
'discerning' is the definition.
(similar in meaning)
'terribly pious caprices' is the wordplay.
'terribly' indicates anagramming the letters.
'pious'+'caprices'='piouscaprices'
'piouscaprices' anagrammed gives 'PERSPICACIOUS'.
'but' is the link.
(Other definitions for perspicacious that I've seen before include "Astute" , "Discerning" , "Insightful" .)