Repose cut short -- it's bad weather (6)
I believe the answer is:
resist
'weather' is the definition.
(thesaurus)
'repose cut short it's bad' is the wordplay.
'repose' becomes 'rest' ('rest' can be a synonym of 'repose').
'cut short' means to remove the last letter.
'bad' indicates an anagram.
'rest' with its last letter taken off is 'res'.
'its' anagrammed gives 'ist'.
'res'+'ist'='RESIST'
(Other definitions for resist that I've seen before include "turn down" , "Don't give in" , "Withstand, struggle against" , "'Withstand, fight against (6)'" , "Sister (anag)" .)