A note of asperity (5)
I believe the answer is:
sharp
'a note' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for sharp that I've seen before include "Hurtful" , "Acute - very keen" , "Cutting; acidic" , "Acidic; pointed" , "Unscrupulous character" .)