The French shelter is hidden (6)
I believe the answer is:
latent
'is hidden' is the definition.
(latent can mean hidden or unused)
'the french shelter' is the wordplay.
'the french' becomes 'la' (one of the French words for 'the').
'shelter' becomes 'tent' (canvas shelter).
'la'+'tent'='LATENT'
(Other definitions for latent that I've seen before include "Hidden (potential)" , "Hidden, dormant" , "Existing but not yet developed, say ability" , "There but not yet effective" , "Existing but not yet active or visible" .)