Tap lightly (3)
I believe the answer is:
pat
'tap lightly' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pat that I've seen before include "Affectionate gesture - postman" , "Hit lightly" , "Gentle stroke of the hand with fluent repetition" , "Conveniently; light touch" , "Touch with hand" .)