This article is devoted to a number of specific historical meanings the word took, in approximate historical order.
Roman Emperor 
Princeps (in this sense usually translated as "First Citizen") was an official title of a Roman Emperor as the title determining the leader in Ancient Rome at the beginning of the Roman Empire. It created the principate Roman imperial system.
This usage of "princeps" derived from the position of Princeps Senatus, the "first among equals" of the Senate. The princeps senatus (plural principes senatus) was the first member by precedence of the Roman Senate.
It was first given as a special title to Caesar Augustus in 27 BC, who saw that use of the titles rex (king) or dictator would create resentment amongst senators and other influential men, who had earlier demonstrated their disapproval by supporting the assassination of Julius Caesar. While Augustus had political and military supremacy, he needed the assistance of his fellow Romans to manage the Empire. In his Res Gestae, Augustus claims auctoritas for the princeps (himself).
For a comprehensive list of other official Roman titles used for the office of emperor see Roman Emperor. These titles included imperator, Augustus, Caesar, and later dominus (lord) and basileus (the Greek word for "sovereign"). The word Emperor itself is derived from the Roman title 'imperator', which was a very high, but not exclusive, military title until Augustus began to use it as his praenomen.
The Emperor Diocletian (285-305), the father of the Tetrarchy, was the first to stop referring to himself as "princeps" altogether, calling himself 'dominus' (lord, master), thus dropping the pretense that emperor was not truly a monarchical office. The period when the emperors that called themselves princeps ruled - from Augustus to Diocletian - is called "the Principate", while no later than under Diocletian began "the Dominate" period.
Ancient Rome knew another kind of 'princely' principes too, like 'princeps iuventutis' ("the first amongst the young"), which in the early empire was frequently bestowed on eligible successors to the emperor, especially from his family. It was first given to Augustus' adoptive sons Gaius and Lucius.
Roman administration 
Princeps is also the (official) short version of Princeps officii, the chief of an officium (the office staff of a Roman dignitary) -
- See Principes (legionary heavy infantry soldier)
- centurio(n) in command of a unit or administrative office.
- Princeps ordinarius vexillationis: centurion in command of a vexillatio (detachment).
- Princeps peregrinorum ("commander of the foreigners"): centurion in charge of troops in the castra peregrina (military base at Rome for personnel seconded from the provincial armies)
- Princeps prior: Centurion commanding a manipulus (unit of two centuries) of principes (legionary heavy infantry).
- Princeps posterior: deputy to the Princeps prior
- Princeps praetorii : centurion attached to headquarters.
Princeps was also used as defining second part of various other military titles, such as Decurio princeps, Signifer princeps (among the standard-bearers). See also Principalis (as in Optio principalis): NCO.
Nobiliary legacy 
"Princeps" is the root and Latin rendering of modern words as the English title and generic term prince (see that article, also for various equivalents in other languages), as the Byzantine version of Roman law was the basis for the legal terminology developed in feudal (and later absolutist) Europe.
Non-Roman meaning 
- Latin binomial abbreviations for species
- A. princeps (disambiguation)
- B. princeps
- C. princeps (disambiguation)
- E. princeps
- G. princeps (disambiguation)
- H. princeps
- J. princeps
- K. princeps
- L. princeps
- M. princeps
- O. princeps (disambiguation)
- P. princeps (disambiguation)
- R. princeps (disambiguation)
- S. princeps (disambiguation)
- T. princeps (disambiguation)
- X. princeps (disambiguation)
- Z. princeps
- Cattleya walkeriana var. princeps, a synonym for Cattleya walkeriana, an orchid species
- Emberiza flaviventris princeps, a bird subspecies found in Angola and Namibia
- Heterohyrax brucei princeps, a mammal subspecies found in Africa
- In the Foundation series by Isaac Asimov, First Citizen is the title taken by the Mule and his successors in their position as leader of the Union of Worlds.
- Princeps is the name of a dog that Brother Priad meets in the Warhammer 40,000 book Brothers of the Snake.
- Princeps is the title for the captain of a Titan, a massive humanoid war machine in the tabletop wargame Warhammer 40,000.
- In the book series Codex Alera by Jim Butcher, Princeps is the title given to the crown prince of the empire of Alera. It is also used in the title of the fifth book in the series, Princeps' Fury.
- In the Star Trek: Infinity's Prism book Seeds of Dissent by James Swallow, "Princeps" is the title for 'Commander' Julian Bashir of the warship Defiance which exists in an alternate universe from the more familiar 24th Century envisioned from the television series Star Trek: Deep Space Nine.
- Charlton T. Lewis, Charles Short (1897). "princeps, cĭpis, adj.". A Latin Dictionary. Retrieved 2009-04-21.
- Grant, p. 62
- Africa, Thomas (1991). The Immense Majesty: A History of Rome and the Roman Empire. Harlan Davidson, Inc. p. 219.
See also 
- Grant, Michael, The Twelve Caesars, Michael Grant Publications 1975, ISBN 0-684-14402-6