Could be an extreme show of anger or just moderate (6)
I believe the answer is:
temper
'moderate' is the definition.
(synonyms)
'could be an extreme show of anger' is the wordplay.
I cannot quite see how this works, but
'an' could be 'per' (synonymous as in 'once an hour', 'once per hour') and 'per' is found in the answer.
The remaining letters 'tem' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'or just' acts as a link.
Can you help me to learn more?
(Other definitions for temper that I've seen before include "Harden with heat and water" , "Moderate - anger" , "Lose it and lose control" , "Irritability" , "Moderate or soften the effects of" .)