Mean, partner? As a rule (8)
I believe the answer is:
normally
'as a rule' is the definition.
(thesaurus)
'mean partner?' is the wordplay.
'mean' becomes 'norm' (I've seen this before).
'partner?' becomes 'ally' (I've seen this in other clues).
'norm'+'ally'='NORMALLY'
(Other definitions for normally that I've seen before include "Ordinarily, usually" , "in standard fashion" , "Naturally" , "By and large" , "In the ordinary or typical way" .)