Quick to provoke (6)
I believe the answer is:
prompt
This clue is a double definition.
'quick' is the first definition.
(I know that immediate can be written as prompt)
'provoke' is the second definition.
(thesaurus)
'to' acts as a link.
(Other definitions for prompt that I've seen before include "Help struggling actor" , "Bring about; timely" , "Dead on time" , "Punctual; instigate" , "Spurs do this" .)