Vex, annoy (3)
I believe the answer is:
irk
This clue is a double definition.
'vex' is the first definition.
(I've seen this in another clue)
'annoy' is the second definition.
(I've seen this before)
(Other definitions for irk that I've seen before include "Severely annoy" , "upset" , "Annoy in quirky way" , "Wind up" , "Bug" .)