Sensible MP with a tragic undoing (9)
I believe the answer is:
pragmatic
'sensible' is the definition.
(thesaurus)
'mp with a tragic undoing' is the wordplay.
'with' says to put letters next to each other.
'undoing' indicates anagramming the letters.
'mp'+'a'+'tragic'='mpatragic'
'mpatragic' anagrammed gives 'PRAGMATIC'.
(Other definitions for pragmatic that I've seen before include "Practical" , "Down-to-earth" , "Realistic" , "for best results?" , "Matter-of-fact" .)