Pater familias
The pater familias, also written as paterfamilias (plural patres familias) was the head of a Roman family. The term is Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 for "father of the family" or the "owner of the family estate". The form is irregular and archaic
In language, an archaism is the use of a form of speech or writing that is no longer current. This can either be done deliberately or as part of a specific jargon or formula...

 in Latin, preserving the old genitive ending in -as (see Latin declension
Latin declension
Latin is an inflected language, and as such has nouns, pronouns, and adjectives that must be declined in order to serve a grammatical function. A set of declined forms of the same word pattern is called a declension. There are five declensions, which are numbered and grouped by ending and...

). The pater familias was always a Roman citizen.

Roman law
Roman law
Roman law is the legal system of ancient Rome, and the legal developments which occurred before the 7th century AD — when the Roman–Byzantine state adopted Greek as the language of government. The development of Roman law comprises more than a thousand years of jurisprudence — from the Twelve...

 and tradition (mos maiorum
Mos maiorum
The mos maiorum is the unwritten code from which the ancient Romans derived their social norms. It is the core concept of Roman traditionalism, distinguished from but in dynamic complement to written law. The mos maiorum The mos maiorum ("ancestral custom") is the unwritten code from which the...

) established the power of the pater familias within the community of his own extended familia.