Something that rouses to action (8)
I believe the answer is:
stimulus
'something that rouses to action' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for stimulus that I've seen before include "Prod or incentive" , "Fillip" , "Incentive, provocation" , "Something that rouses to action" , "Cause of a response" .)