Percussion instrument might be integral (8)
I believe the answer is:
triangle
'percussion instrument' is the definition.
(I know that triangle is a type of percussion instrument)
'might be integral' is the wordplay.
'might be' indicates anagramming the letters (I've seen this in other clues).
'integral' is an anagram of 'TRIANGLE'.
(Other definitions for triangle that I've seen before include "diamond cut in half?" , "Integral part of common geometric figure" , "Three-sided polygon" , "Integral (anag) - geometrical shape" , "Alerting (anag)" .)