Today we’re looking at the words for arrows and related things in Celtic languages.

Old Irish (Goídelc)	saiget [ˈsa.ɣʲəd] = arrow, dart, javelin saigetbolc = quiver saiget geláin (flash of) ligthning
Middle Irish (Gaoidhealg)	saiget = arrow, dart, javelin
Irish (Gaeilge)	saighead [sˠəid̪ˠ/sˠeːd̪ˠ] = arrow, bolt, shaft, dart, pang, incitation saigheadmhar = arrow-like, sharp, piercing saighdeoir = archer, bowman, inciter saighdeoireacht = archery, (act of) spearing (fish)
Scottish Gaelic (Gàidhlig)	saighead [sajəd] = arrow, stabbing pain, knot (in wood) saigheadair [sajədɪrʲ] = arrow-maker, archer
Manx (Gaelg)	side = arrow, bolt, dart, shaft sideyr = archer sideyraght / sideyrys = archery
Proto-Brythonic	*saɣeθ = arrow
Middle Welsh (Kymraec)	saeth = arrow
Welsh (Cymraeg)	saeth [saːɨ̯θ/sai̯θ] = arrow saethu = to shoot, fire, hit (a target), go shooting saethwr /saethydd = archer, bowman, shooter, marksman striker saethol = shooting, darting, radiating saethiad = shooting, shot, blast, projection, squirt, jet
Middle Cornish	seth = arrow
Cornish (Kernewek)	seth = arrow setha = to shoot sether = archer sethigow = darts
Middle Breth	saez = arrow
Breton (Brezhoneg)	saezh = arrow, sunbeam saezhataer / saezhour = Sagittarius

Etymology: from the Latin sagitta (arrow, shaft, bolt), proabably from a pre-Latin Mediterranean language [source].

From the same root we get the Latin word sagittārius (armed with a bow and arrows; archer, bowman, fletcher) which became Sagittarius (a sign of the zodiac) and sagittary (centaur, archer, Sagittarius) in English [source].

Words marked with a * are reconstructions.

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