Medieval guitar (4)
I believe the answer is:
lute
'medieval guitar' is the definition.
(medieval stringed instrument)
This is the entire clue.
(Other definitions for lute that I've seen before include "clay" , "Play instrument" , "Plucked instrument; a sealant" , "Elizabethan stringed instrument" , "Plucked, pear-shaped instrument" .)