Because, per se, it means "to defame" (7)
I believe the answer is:
asperse
'to defame' is the definition.
(synonyms)
'because per se' is the wordplay.
'because' becomes 'as' (I've seen this in other clues).
'as'+'per'+'se'='ASPERSE'
'it means' is the link.
(Other definitions for asperse that I've seen before include "Slander, spread false rumours about - as peers may?" , "Spares E. only to slander him" , "Slander or calumniate" , "See spar could slander oddly" , "Accuse falsely" .)