Corrupt PM, say, needing your compassion (8)
I believe the answer is:
sympathy
'compassion' is the definition.
(I've seen this in another clue)
'corrupt pm say needing your' is the wordplay.
'corrupt' indicates an anagram.
'needing' is a charade indicator (letters next to each other).
'your' becomes 'thy' ('thy' historically meant 'your').
'pm'+'say'='pmsay'
'pmsay' is an anagram of 'sympa'.
'sympa'+'thy'='SYMPATHY'
(Other definitions for sympathy that I've seen before include "Feeling of pity and understanding towards another's difficulty" , "agreement" , "Fellow feeling, understanding" , "Fellow-feeling, compassion" , "Feeling like another" .)