Peevishness I shall moderate (3,6)
I believe the answer is:
ill temper
'peevishness' is the definition.
The definition and answer can be both feelings as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'i shall moderate' is the wordplay.
'i shall' becomes 'ill' (contraction of 'I will').
'moderate' becomes 'temper' (synonyms).
'ill'+'temper'='ILL TEMPER'
Can you help me to learn more?
(Other definitions for ill temper that I've seen before include "black humour" , "Irritability" , "Surliness" .)