Stepmother lets off shot in fit of rage (6)
I believe the answer is:
temper
'rage' is the definition.
(temper means anger or rage)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for temper that I've seen before include "Mood or hardness of metal" , "Frame of mind" , "Moderate - anger" , "Moderate or soften the effects of" , "Irritability" .)