Address bad ad with deceit (8)
I believe the answer is:
dedicate
'address' is the definition.
(thesaurus)
'bad ad with deceit' is the wordplay.
'bad' indicates anagramming the letters.
'with' is a charade indicator (letters next to each other).
'ad' put after 'deceit' is 'deceitad'.
'deceitad' anagrammed gives 'DEDICATE'.
(Other definitions for dedicate that I've seen before include "Commit" , "Devote to a special purpose, say time or energy" , "Inscribe or give over to" , "Devote, address, to" , "Devote to a sacred person or use" .)