Moderate is consumed by irritation (9)
I believe the answer is:
temperate
'moderate' is the definition.
('temperate' can be similar in meaning to 'moderate')
'consumed by irritation' is the wordplay.
'consumed' becomes 'ate' (eating is a kind of consuming).
'by' says to put letters next to each other.
'irritation' becomes 'temper' ('temper' can be a synonym of 'irritation').
'ate' put after 'temper' is 'TEMPERATE'.
'is' acts as a link.
(Other definitions for temperate that I've seen before include "Abstemious" , "sober" , "even" , "Continent" , "Controlled" .)