Curt; sudden (6)
I believe the answer is:
abrupt
I believe this is a double definition.
'curt' is the first definition.
(both can mean rudely brief)
'sudden' is the second definition.
(similar in meaning)
(Other definitions for abrupt that I've seen before include "Rough and quick" , "Curt, sharp" , "Unexpected -- precipitous" , "Offhand" , "Impolite" .)