Slander from French celebrity (6)
I believe the answer is:
defame
'slander' is the definition.
(synonyms)
'from french celebrity' is the wordplay.
'from french' becomes 'de' ('from' in French).
'celebrity' becomes 'fame' (celebrity can mean the quality of being famous).
'de'+'fame'='DEFAME'
(Other definitions for defame that I've seen before include "Traduce" , "Asperse" , "libel" , "Damage (someone's) reputation" , "to pretetrate slander?" .)