Concise Bible Dictionary:

This word is used in scripture indefinitely for any one in authority, there being seven Hebrew words so translated. In the New Testament are
1. πράκτωρ, from “to do or act,” it occurs only in Luke 12:58. It is used for the officer appointed to exact the money adjudicated by the judge.
2. ὑπηρἐτης, literally “an under-rower,” a subordinate officer, who assisted the priests and the Roman governors (Matt. 5:25; John 7:32,45-46; John 18:3-22; John 19:6; Acts 5:22,26). It is also translated “minister” and “servant.”