Do not include altering main ruling (8)
I believe the answer is:
dominant
'ruling' is the definition.
(I've seen this in another clue)
'do not include altering main' is the wordplay.
'not' becomes 'nt' (synonyms).
'include' indicates putting letters inside.
'altering' indicates an anagram.
'do'+'nt'='dont'
'main' is an anagram of 'mina'.
'dont' going around 'mina' is 'DOMINANT'.
(Other definitions for dominant that I've seen before include "Having power and influence over others" , "Most influential; fifth of scale" , "Exercising influence or control" , "Prevailing or in a commanding position" , "Authoritative" .)