peth₂-r̥
“father (nominal)”Source of Latin pater, English father, patron, patrimony
Nominal root for father, yielding Latin pater and English father, patron, patrimony, patriarch.
Discussion
The Proto-Indo-European form *peth₂-r̥ is the kinship term for "father" in its nominal form, one of the most securely reconstructed words in the proto-lexicon. The word belongs to the class of r/n-stem kinship nouns (alongside *méh₂tēr "mother", *bʰréh₂tēr "brother", *dʰugh₂tḗr "daughter") that form the core of the Indo-European family vocabulary. The laryngeal *h₂ is confirmed by its effects on the adjacent vowel.
In Germanic, the initial *p became *f by Grimm's Law, and the word descended into Old English fæder, which became modern English father. German Vater, Dutch vader, and Swedish fader are close cognates. The Grimm's Law shift of *p to *f is one of the defining sound changes of the Germanic branch and is perfectly illustrated by this word: compare English father with Latin pater, where the *p was preserved.
Latin pater "father" has been enormously productive in English: paternal, patriarch (father-ruler), patron (a fatherly protector), patronise, patrimony (a father's inheritance), patrician (of the father-class), and the given name Patrick (from patricius "of noble father"). The word padre (borrowed from Spanish/Italian) and pope (from papa, an informal word for father) are further extensions.
Greek patēr "father" gave English patriot (one devoted to the fatherland) and patronymic (a name derived from the father). Sanskrit pitár- "father" is a transparent cognate, as are Old Irish athir, Lithuanian pater, and Armenian hayr.
The Proto-Indo-European kinship terms were not merely descriptive labels but encoded social roles and legal obligations. The *peth₂-r̥ was not just a biological parent but the head of the household, the holder of authority, and the representative of the family before the community. The word's survival in virtually every Indo-European language testifies to the centrality of paternal authority in the proto-society.