Irritate, worry (3)
I believe the answer is:
vex
This clue is a double definition.
'irritate' is the first definition.
(I know that irritate can be written as vex)
'worry' is the second definition.
(I know that worry can be written as vex)
(Other definitions for vex that I've seen before include "upset" , "Irritate, annoy" , "Irk" .)