Accidental piercing (5)
I believe the answer is:
sharp
This clue is a double definition.
'accidental' is the first definition.
(thesaurus)
'piercing' is the second definition.
(similar in meaning)
(Other definitions for sharp that I've seen before include "music feature" , "Above true pitch; stylish" , "Acidic; note" , "Hurtful" , "Cutting; note" .)