Moderate a rich concoction (5)
I believe the answer is:
chair
'moderate' is the definition.
(I know that moderate can be written as chair)
'a rich concoction' is the wordplay.
'concoction' is an anagram indicator.
'a'+'rich'='arich'
'arich' with letters rearranged gives 'CHAIR'.
(Other definitions for chair that I've seen before include "rocker?" , "Prof's post; meeting leader" , "Preside, guide meeting" , "Something with legs" , "Supporter" .)