The French island certainly offers relaxation (7)
I believe the answer is:
leisure
'relaxation' is the definition.
(leisure is a kind of relaxation)
'the french island certainly' is the wordplay.
'the french' becomes 'le' ().
'island' becomes 'i'.
'certainly' becomes 'sure' (synonyms).
'le'+'i'+'sure'='LEISURE'
'offers' is the link.
(Other definitions for leisure that I've seen before include "Rest, relaxation" , "Recreation time" , "Time away from work" , "idle hours" , "Time when not working" .)