Fillip, stimulus (5)
I believe the answer is:
boost
I believe this clue is a double definition.
'fillip' is the first definition.
(I've seen this before)
'stimulus' is the second definition.
(thesaurus)
(Other definitions for boost that I've seen before include "Increase or encourage(ment)" , "Promote" , "Help to increase" , "Raise" , "Push upwards, help" .)