Moderate fool and unionist get on (7)
I believe the answer is:
assuage
'moderate' is the definition.
(I've seen this before)
'fool and unionist get on' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'and' is a charade indicator (letters next to each other).
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'get on' becomes 'age' (synonyms).
'ass'+'u'+'age'='ASSUAGE'
(Other definitions for assuage that I've seen before include "allay hunger perhaps" , "Appease, calm" , "Satisfy (a desire)" , "'Make less severe, pain say (7)'" , "Soothe, make less severe" .)