Blew off steam (6)
I believe the answer is:
vented
'blew off steam' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for vented that I've seen before include "Discharged" , "Expressed freely, say anger" , "Aired - say grievance or anger" , "Let (air/gas) out" , "Aired, gave outlet to - say anger" .)