Stimulus quietly provided with stick (4)
I believe the answer is:
prod
'stimulus' is the definition.
(I've seen this before)
'quietly provided with stick' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'provided with' means one lot of letters go next to another.
'stick' becomes 'rod' (I've seen this before).
'p'+'rod'='PROD'
(Other definitions for prod that I've seen before include "Poke (with a finger, etc)" , "Give a reminder" , "Poke with forefinger, stimulate" , "Motivate; jab" , "Remind (with elbow or stick?)" .)