Corrupt French noble appears in court (6)
I believe the answer is:
seduce
'corrupt' is the definition.
(thesaurus)
'french noble appears in court' is the wordplay.
'french noble' becomes 'duc' ('duke' in French).
'appears in' means one lot of letters goes inside another.
'court' becomes 'see' (both can mean to date somebody).
'duc' placed into 'see' is 'SEDUCE'.
(Other definitions for seduce that I've seen before include "mislead" , "Persuade to be false" , "Debauch" , "Lure or entice into bad behaviour" , "get into bed?" .)