Piercing scream (6)
I believe the answer is:
shriek
'piercing scream' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for shriek that I've seen before include "Scream of pain or delight" , "Sharp piercing cry" , "Short piercing scream" , "Hikers (anag.)" , "Shrill cry or scream" .)