Small four-stringed guitar (7)
I believe the answer is:
ukulele
'small four-stringed guitar' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ukulele that I've seen before include "Stringed instrument" , "Small Hawaiian guitar" , "George Formby's instrument" , "One needs pluck in this" , "Small guitar as played by George Formby" .)