French antonym shows how to charm (7)
I believe the answer is:
enchant
'how to charm' is the definition.
(I know that becharm is a is a more specific form of the action of enchant)
'french antonym shows' is the wordplay.
'shows' indicates a hidden word.
'ENCHANT' can be found hidden inside 'french antonym'.
(Other definitions for enchant that I've seen before include "Fascinate - delight" , "Appeal" , "Delight, cast spell over" , "Captivate, charm" , "transport" .)