Quiet, angry corsair (6)
I believe the answer is:
pirate
'corsair' is the definition.
(I've seen this in another clue)
'quiet angry' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'angry' becomes 'irate' (irate can mean angry or annoyed).
'p'+'irate'='PIRATE'
(Other definitions for pirate that I've seen before include "Robber on the high scas" , "Freebooter" , "fake" , "Cornishman maybe" , "Sea raider" .)