Proto-Indo-European Roots

Root/Stem: *awo-, *awio-

Meanings: mother's brother

Cognates (32):

Hellenic Greek aia (ground, motherland)

Italic Latin avus (grandfather)

Celtic Common Celtic *avios (related to grandfather); >
Old Irish aue, haue (grandson), Irish ó (grandson), Welsh ewythr (mother's brother), Cornish euitor, Breton eontr

Indic

Dardic & Nuristani

Iranian

Anatolian

Tocharian

Armenian Armenian hav, gen. havu (grandfather)

Balkan

Germanic Common Germanic *awón-, *awé-, *awun-; >
Gothic awó (grandmother), Old Icelandic ái (great grandfather), afi (grandfather), Old English & Old Saxon éam (grandfather), Old Frisian ém, Old High German óheim (mother's brother), Middle Low German óm;
German Oheim (mother's brother), Dutch oom (grandfather)

Baltic Lithuanian ava (mother's brother's wife), avynas (mother's brother), Old Prussian awis

Slavic Common Slavic *ujï (mother's brother), >
Ukrainian vuj, Old Serbian uika, Bulgarian uiko, Serbo-Croatian ujac, Slovene & Czech & Slovak ujec, Polish wuj (uncle), Lower Sorbian hujk (uncle, cousin), Russian uj (mother's brother)

Notes: The term is rather dark, and its origin and exact meaning are not quite clear yet. It is obvious, however, that it denoted kinship. Most of modern Indo-European languages do not preserve the original complicated system of kinship terms: uncle in English means both 'mother's brother' and 'father's brother', while in Proto-Indo-European there used to be two different words. The same goes for other terms: 'sister's husband', 'son's wife', etc.
The presence of the initial *H- (laryngeal) is also a question.

*Root/Stem:*	awo-, awio-

*Meanings:*	mother's brother

*Cognates (32):*
Hellenic	Greek *aia* (ground, motherland)
Italic	Latin *avus* (grandfather)
Celtic	Common Celtic avios (related to grandfather); > Old Irish aue, haue* (grandson), Irish ó (grandson), Welsh *ewythr* (mother's brother), Cornish *euitor, Breton eontr*
Indic
Dardic & Nuristani
Iranian
Anatolian
Tocharian
Armenian	Armenian *hav,* gen. *havu* (grandfather)
Balkan
Germanic	Common Germanic awón-, awé-, awun-; > Gothic awó* (grandmother), Old Icelandic ái (great grandfather), *afi* (grandfather), Old English & Old Saxon *éam* (grandfather), Old Frisian ém, Old High German *óheim* (mother's brother), Middle Low German óm; German *Oheim* (mother's brother), Dutch *oom* (grandfather)
Baltic	Lithuanian *ava* (mother's brother's wife), *avynas* (mother's brother), Old Prussian *awis*
Slavic	Common Slavic ujï (mother's brother), > Ukrainian vuj, Old Serbian uika, Bulgarian uiko, Serbo-Croatian ujac, Slovene & Czech & Slovak ujec, Polish wuj* (uncle), Lower Sorbian *hujk* (uncle, cousin), Russian uj (mother's brother)

Notes:	The term is rather dark, and its origin and exact meaning are not quite clear yet. It is obvious, however, that it denoted kinship. Most of modern Indo-European languages do not preserve the original complicated system of kinship terms: uncle in English means both 'mother's brother' and 'father's brother', while in Proto-Indo-European there used to be two different words. The same goes for other terms: 'sister's husband', 'son's wife', etc. The presence of the initial *H- (laryngeal) is also a question.