Moderate hated being exposed as abstemious (9)
I believe the answer is:
temperate
'abstemious' is the definition.
(similar in meaning)
'moderate hated being exposed' is the wordplay.
'moderate' becomes 'temper' (synonyms).
'being exposed' means to look at the middle letters (the inside of the word is exposed).
The central letters of 'hated' are 'ate'.
'temper'+'ate'='TEMPERATE'
'as' is the link.
(Other definitions for temperate that I've seen before include "comfortably warm?" , "with balmy climate" , "With mild climate" , "Abstemious" , "It is reasonable" .)