Loses one's temper (6)
I believe the answer is:
erupts
'loses one's temper' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for erupts that I've seen before include "Blows up like volcano" , "Explodes" , "Breaks out abruptly" , "Breaks out suddenly" , "loses temper?" .)