Weather in Chartres is terrible (6)
I believe the answer is:
resist
'weather' is the definition.
(thesaurus)
'in chartres is terrible' is the wordplay.
'in' indicates a hidden word.
'RESIST' is hidden within 'chartres is terrible'.
(Other definitions for resist that I've seen before include "Stand up to, fight against" , "Check; withstand" , "Refuse to comply" , "Don't give in" , "Take stand against, oppose" .)