U2 singer holds good instrument (5)
I believe the answer is:
'instrument' is the definition.
(I know that bongo is a type of drum)
'u2 singer holds good' is the wordplay.
'u2 singer' becomes 'Bono' (Bono is the frontman of U2).
'holds' indicates putting letters inside.
'good' becomes 'g' (abbreviation).
'bono' placed around 'g' is 'BONGO'.
(Other definitions for bongo that I've seen before include "Drum between the knees" , "Small Cuban drum" , "One of a pair of drums" , "Bucket-shaped drum - rare spiral-horned antelope" , "Hand-played drum" .)