Poke with a finger (4)
I believe the answer is:
prod
'poke with a finger' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for prod that I've seen before include "Poke with forefinger, stimulate" , "Push with pointed instrument" , "Provide stimulation" , "Induce action (with stick etc?)" , "Drop (anag.)" .)