It's used to pluck guitar strings (8)
I believe the answer is:
plectrum
'it's used to pluck guitar strings' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for plectrum that I've seen before include "Object used to pluck stringed instrument" , "It's used to pluck, a guitar say" , "Device for playing guitar" , "Guitarist's aid" , "Guitar pick" .)