Words for nine and related things in Celtic languages:
| Proto-Celtic | *nowan = nine *naumetos = ninth |
|---|---|
| Gaulish | *nau = nine nametos = ninth |
| Old Irish (Goídelc) | noí [n͈oːi̯] = nine nómad = ninth nónbor = nine people noínden = nine days |
| Middle Irish (Gaoidhealg) | noí, noi = nine nómad, nomad = ninth nónbor = nine people noínden = nine days noíchtige = a period of 29 days nócha, nocha, nochat = ninety |
| Irish (Gaeilge) | naoi [n̪ˠiː/n̪ˠɰiː] = nine (an) naoú = ninth naonúr = nine people naoi déag = nineteen nócha = ninety naoichodach = ninefold, having nine parts |
| Scottish Gaelic (Gàidhlig) | naoi(dh) [n̪ˠɯj] = nine naodh [n̪ˠɯːɣ] = nine naoitheamh [n̪ˠɤjəv] (9ᵐʰ) = ninth (9ᵗʰ) naoinear [n̪ˠɯːn̪ʲər] = nine (people) naoi deug = nineteen naochad [n̪ˠɯːxəd] = ninety naoidh-fillte = nonuple, ninefold, nine-ply |
| Manx (Gaelg) | nuy [nɛi/niː] = nine (yn) nuyoo = (the) ninth nuy jeig = nineteen nuy-cheayrtyn, nuy-filley = ninefold nuy-uillinagh = nonagonal, nonagon |
| Proto-Brythonic | *naw [n͈oːi̯] = nine *nọβ̃ed = ninth |
| Old Welsh | naw = nine |
| Middle Welsh (Kymraec) | nav, nau, naw = nine navuet, nauuet, nawued, nawuet = ninth naw deg, naw-deg = ninety nawkan, naw cant, nawcant = nine hundred, many, numerous naw ugein(t) = 180 nawbann, nowban = (having) nine syllables (in Welsh poetry) nawwell, nawell = nine times better (than), much better naun, nawn, naon = the ninth hour of the day naw nyn, nawnyn = nine men |
| Welsh (Cymraeg) | naw [naːu̯/nau̯] = nine nawfed [ˈnau̯vɛd/ˈnau̯vad] (9fed) = ninth, one of nine, nones (in Roman calendar) deunaw = eighteen (two nines) naw deg = ninety nawcant = nine hundred, many, numerous nawban, naw ban = (having) nine syllables (in Welsh poetry) nawell = nine times better (than), much better nawn = the ninth hour of the day (approx. 3pm) midday, nooon, afternoon nawnbryd = evening meal, dinner, supper nawnyn, naw nyn = nine men nawplyg = ninefold |
| Middle Cornish (Cernewec) | naw = nine nawnzac, nawntek, nownsec, nowndzhak = nineteen naiv cans = nine hundred |
| Cornish (Kernewek) | naw = nine nawves = ninth nownsek = nineteen nowsegves = nineteenth |
| Old Breton | nau = nine |
| Middle Breton (Brezonec) | nau, nao, naou, naff, nauë, naü = nine navet = ninth nauntec, nantec, nandec = nineteen naontecvet, nandecvèd, naontekved, naoñteget = nineteenth nao ugent = 180 |
| Breton (Brezhoneg) | nav [ˈnaw] = nine navet = ninth naontek = nineteen |
Etymology: from Proto-Indo-European *h₁néwn̥ (nine) and *h₁newn̥nós (ninth) [source].
English words from the same roots include nine, and words beginning with ennea-, such as enneagon (a 9-sided polygon) and enneastyle (having 9 columns) [source].
Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, eDIL – Electronic Dictionary of the Irish Language, In Dúil Bélrai English – Old Irish glossary, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Gerlyvyr Cernewec, Dictionaire Favereau, TermOfis, Le dictionnaire diachronique du breton, Geriafurch, English – ProtoCeltic WordList (PDF), Etymological Dictionary Of Proto Celtic
No, Simon, the two Manx words you quote definitely don’t mean ‘quadruple’. Even the old Manxies were not mathematically challenged to that extent!
‘nawn’ in Welsh is a borrowing from Latin ‘nōna (hōra)’ and is therefore not related (directly) to the other Welsh nouns listed (as in the others are derived organically in Welsh as opposed to being borrowings).