Unusual risk causes annoyance (4)
I believe the answer is:
irks
'causes annoyance' is the definition.
Although both the answer and definition are verbs in their -s form, I can't understand how they can define each other.
'unusual risk' is the wordplay.
'unusual' indicates an anagram.
'risk' with letters rearranged gives 'IRKS'.
Can you help me to learn more?
(Other definitions for irks that I've seen before include "Annoys, vexes" , "'Irritate, annoy (4)'" , "Galls" , "Annoys, irritates" .)