Electric guitar accessory (3)
I believe the answer is:
amp
'electric guitar accessory' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for amp that I've seen before include "A flow of one coulomb per second" , "In short, unit for measuring electric current" , "Sound-boosting piece of equipment (abbr)" , "Device to up the sound of an electric guitar (abbr)" , "Current measure" .)