Accident; disaster (6)
I believe the answer is:
mishap
I believe this clue is a double definition.
'accident' is the first definition.
(mishap is a kind of accident)
'disaster' is the second definition.
(thesaurus)
(Other definitions for mishap that I've seen before include "An accident, piece of bad luck" , "Blow" , "Contretemps" , "Stroke of bad luck" , "Unlucky development" .)