Slight pains: sore bum (9)
I believe the answer is:
aspersion
'slight' is the definition.
'pains sore bum' is the wordplay.
'bum' indicates an anagram (bum can mean faulty or wrong).
'pains'+'sore'='painssore'
'painssore' is an anagram of 'ASPERSION'.
(Other definitions for aspersion that I've seen before include "No praises (anag) - disparaging remark" , "Negative comment" , "Cast this slur" , "Slander" , "Defamatory suggestion" .)