princeps, principal chief).
originally: any leading Roman citizen
First citizen, leader or best leader.
first in rank, leader, a title assumed by Augustus to denote his position and then taken by later emperors.
Also known as first citizen,Princeps was the title Augstus took upon his rise to power(and would be used by many of his sucessors). This term made the chief distinction from the word "king" because, unlike a king, the princeps was not above the people but instead was just the "first citizen" who left the real power to the senate.In actual fact, the princeps held all power and the senate just had the appearance of real power.
The Latin word Princeps (plural: principes) means "the first".