In slander I detect insult (6)
I believe the answer is:
deride
'insult' is the definition.
(thesaurus)
'in slander i detect' is the wordplay.
'in' indicates the answer is hidden within the clue.
'DERIDE' is hidden in the letters of 'slander i detect'.
(Other definitions for deride that I've seen before include "'Mock, sneer at (6)'" , "Jeer, belittle" , "Laugh at or make fun of" , "Speak of with contempt" , "Disparage" .)