Words for swallows, swifts and martins in Celtic languages.

Proto-Celtic	*wesnālā = swallow
Old Irish (Goídelc)	ainnel, fannall = swallow
Middle Irish (Gaoidhealg)	áilleóc, fainleóc = swallow
Irish (Gaeilge)	fáinleog, áinleóg = swallow
Scottish Gaelic (Gàidhlig)	(f)ainnleag [(f)ãĩn̪ʲl̪ʲag] = swallow, martin, storm(y) petrel
Proto-Brythonic	*gwennọl = swallow
Old Welsh	guennol = swallow
Middle Welsh (Kymraec)	gwennawl = swallow
Welsh (Cymraeg)	gwennol [ˈɡwɛnɔl] = swallow, martin; weaver’s shuttle
Cornish (Kernewek)	gwennol = swallow
Old Breton	guennol = swallow
Middle Breton	guennel = swallow
Breton (Brezhoneg)	gwennel = swallow

Etymology: from the Proto-Indo-European *wós-r̥/*wés-n̥s (spring) [source].

Irish (Gaeilge)	gabhlán = martin gabhlán-binne = house martin (delichon urbicum)) gabhlán gainimh = sand martin (riparia riparia) gabhlán gaoithe = swift (apus apus)
Scottish Gaelic (Gàidhlig)	gòbhlan [gɔːl̪ˠan] = swallow, martin; prong, small fork gòbhlan-gaoithe [goːl̪ˠan’gɤjə] = barn swallow (hirundo rustica) gòbhlan-gainmhich [goːl̪ˠan gɛnɛvɪç] = sand martin, bank swallow gòbhlan-dubh [goːl̪ˠan du] = (common) swift gòbhlan-mara [goːl̪ˠan marə] = storm(y) petrel (hydrobatidae)
Manx (Gaelg)	gollan = swift, martin; fork gollan geayee = swallow gollan gheinnee = sand martin gollan mooar = swift gollan thie = house martin

Etymology: from the Old Irish gabul (fork, forked branch), from the Proto-Celtic *gablā (fork, branch, gallows), from the Proto-Indo-European *gʰeh₁bʰ- (to grab, take) [source].

Words marked with a * are reconstructions.

Here’s a tune I wrote called The Swallow / Y Wennol:

Sources: Wiktionary, Am Faclair Beag, MacBain’s Dictionary, In Dúil Bélrai English – Old-Irish Glossary, teanglann.ie, On-Line Manx Dictionary, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau