Words for blue / green / grey in Celtic languages.
| Proto-Celtic | *glastos = green, blue |
|---|---|
| Gaulish | *glastom = green, blue |
| Old Irish (Goídelc) | glas [ɡlas] = green, greenish (esp of growing things); blue, green-blue, grey-blue; metallic (colour); ice/frost colour; grey; wan (complexion); bluish, livid, discolored; faded |
| Irish (Gaeilge) | glas [ɡlˠasˠ] = green (grass, politics); grey (horses, cloth, eyes); blue; grey; pale pallid; immature, unseasoned; raw inexperienced |
| Scottish Gaelic (Gàidhlig) | glas [gl̪ˠas] = grey-green; pale, wan, sallow; green, unripe |
| Manx (Gaelg) | glass = green (of nature), verdant, soft, pale, pasty, ashen (colour), grey (of animal), raw, unfledged, sappy, callow (of youth) |
| Proto-Brythonic | *glas = green, blue |
| Welsh (Cymraeg) | glas [ɡlaːs] = blue, azure, sky-blue, greenish blue, sea-green; green, grass-coloured, bluish green, verdant; unripe (of fruit); greyish-blue, slate-coloured, livid, pallid, pale; grey; silver |
| Cornish (Kernewek) | glas [gla:z /glæ:z] = blue, grey, green |
| Breton (Brezhoneg) | glas = blue, green (nature), grey (horse), raw & salty, fresh, bitter, pale |

Words marked with a * are reconstructions.
Etymology
From Proto-Indo-European *ǵʰl̥h₃stós, from *ǵʰelh₃- (green, yellow)
Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau

