Reign
means,


Rule.
Have superior power or uncontrolled dominion over.
Let not sin therefore reign in your mortal body,
that ye should obey it in the lusts thereof. 
Neither yield ye your members
as instruments of unrighteousness unto sin:
but yield yourselves unto God,
as those that are alive from the dead,
and your members as
instruments of righteousness
unto God.

Romans   
6:12-13