Young

Words for young in Celtic languages.

Proto-Celtic *yowankos = young
Old Irish (Goídelc) óc [oːɡ] = young
Irish (Gaeilge) óg [oːɡ / ɔːɡ] = young; junior, minor; new, fresh, early
Scottish Gaelic (Gàidhlig) òg [ɔːg] = young, youthful
Manx (Gaelg) aeg [ɛːɡ] = young, adolescent, immature
Proto-Brythonic *jowank = young
Middle Welsh (Kymraec) ieuanc [ˈjeɨ̯aŋk] = young, juvenille, unmarried
Welsh (Cymraeg) ifanc [ˈɪvaŋk / ˈiːvaŋk] = young, youthful, adolescent; inexperienced, immature; recent; unmarried, newly wed
Middle Cornish yowynk, yonk = young
Cornish (Kernewek) yowynk [‘jɔwɪŋk] = young, juvenille
yonk [jɔˑŋk] = young, juvenille
Middle Breton youanc = young
Breton (Brezhoneg) yaouank = young

Etymology
Possibly from the Proto-Indo-European *h₂yuh₁n̥ḱós (young).

Words marked with a * are reconstructions.

Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau

Good

Words for good in Celtic languages.

Proto-Celtic *matis = good
Old Irish (Goídelc) maith [maθʲ] = good
Irish (Gaeilge) maith [mˠa(h) / mˠaɪ(h)] = good; goodness, kindness; good things; fertility
Scottish Gaelic (Gàidhlig) math [ma] = good, well
Manx (Gaelg) mie [maɪ] = good, nice, moral, fair, pious, ready, goodness, favourable, virtuous, virtue, goodly
Proto-Brythonic *mad = good
Middle Welsh (Kymraec) mad [maːd] = good
Welsh (Cymraeg) mad [maːd] = good, lucky, fortunate, suitable, auspicious, beneficial, virtuous, holy, fair, pleasant, beautiful
Cornish (Kernewek) mas [ma:z / mæ:z] = good, respectable, moral
Middle Breton mat = good
Breton (Brezhoneg) mat / mad [maːd] = good, good product, moral, well (done), sweet

Etymology
From Proto-Indo-European *meh₂tis (ripe, good), from *meh₂- (to ripen, to mature) [source].

Note: mad is not commonly used in modern Welsh. The usual word for good is da.

Words marked with a * are reconstructions.

Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau

Gods, Deities & Days

Words for gods, deities & days in Celtic languages.

Proto-Celtic *dēwos = god, deity, day
*dēwā = goddess
Gaulish deuognata, teuoxtonio-, dēuos, dēwos, dēvona = god
Celtiberian teiuoreikis, deobriga = god
Galician deva = goddess (in river names)
Old Irish (Goídelc) día [dʲiːa̯] = god
Irish (Gaeilge) dia [dʲiə] = god, deity (plural: déithe)
Scottish Gaelic (Gàidhlig) dia [dʲiə] = god (plural: diathan)
Manx (Gaelg) jee = god, deity, godhead (plural: jeeaghyn)
Proto-Brythonic *duɨw [ˈduɨ̯w] = god
Old Welsh duiu = god
Welsh (Cymraeg) duw [dɨu̯ / dɪu̯] = god, the Supreme Being, the Almighty, the Christian Trinity; O God! (plural: duwiau)
Old Cornish duy = god
Cornish (Kernewek) duw [dyˑʊ / diˑʊ] = god (plural: duwow)
Old Breton doi = god
Middle Breton doe = god
Breton (Brezhoneg) doue = god

Etymology
From Proto-Indo-European *deywós (god), from *dyew- (sky, heaven) [source]. The Latin name for the city of Chester, Deva, possibly comes from the same Celtic root [source].

Words marked with a * are reconstructions.

Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau