Select a plectrum (4)
I believe the answer is:
pick
I believe this clue is a double definition.
'select' is the first definition.
(picking is a kind of selecting)
'a plectrum' is the second definition.
('pick' can be a synonym of 'plectrum')
(Other definitions for pick that I've seen before include "Hero of a Dickens novel" , "hacker?" , "The best tool" , "option" , "Play guitar" .)