A person who exercises authority over civilian affairs(noun)
WordNet. Princeton University. 2010.
Use "civil authority" in a sentence
"Williams left for England, committing the civil authority to lords justices and the military command to General Ginkel."
"And sir it is a well known fact, as my colleague has said, that the military is strictly subordinated to civil authority — constituted by it and ameneneable to it for every abuse of its power."
"Spain to extirpate the heresy: There is no ground in the condemnation and death of Priscillian for the charge made against the Church of having invoked the civil authority to punish heretics."