Language used by French in Dieppe (5)
I believe the answer is:
hindi
'language' is the definition.
(Hindi is an example)
'used by french in dieppe' is the wordplay.
'used by' indicates a hidden word.
'HINDI' is hidden in the letters of 'french in dieppe'.
(Other definitions for hindi that I've seen before include "One of India's official languages" , "Language of northern India" , "tongue" , "Indian language" , "It's spoken abroad" .)