Words for land, parish, enclosure in Celtic languages.

Proto-Celtic	*landā = (open) land
Gaulish	landa = land
Old Irish (Goídelc)	land, lann = building, house, land, plot, plate
Middle Irish (Gaoidhealg)	land, lann = building, house, land, plot, plate íarlann = pantry ithlann, ithla = threshing floor, barn, granary, storehouse; garden, orchard
Irish (Gaeilge)	lann = land, ground, plot, house, building (especially a church) bialann = canteen, restaurant leabharlann = library longlann = dockyard réadlann = observatory saotharlann = laboratory
Scottish Gaelic (Gàidhlig)	lann [l̪ˠaun̪ˠ ~ l̪ˠan̪ˠən] = enclosure, enclosed area, precinct; repository; house, church amharc-lann = observatory biadh-lann = canteen, dinning hall, refectory broc-lann = badger’s den, sett long-lann = dockyard fasg-lann = shelter lann-eaglaise = church precinct leabhar-lann = library obair-lann = laboratory suin-lann = dormitory ur-lann = esplanade, green
Manx (Gaelg)	lann = enclosure, habitation lhonglann = dockyard lioarlann = library seyrlann = laboratory reayrtlann = observatory
Proto-Brythonic	*llann [ˈl͈anː] = land, area, plot, sacred place, churchyard
Middle Welsh (Kymraec)	lánn, lann, lan, llann = land
Welsh (Cymraeg)	llan [ɬan] = (parish) church, monastery, heaven, churchyard llan gadeiriol = cathedral llan (y) gwyryfon = nunnery llan y plwyf = parish chuch llandref = village, small town, church village llandy = parsonnage, glebe-house llangeidwad = churchwarden llanaidd = glade-like, open, clear; ecclesiastical, (of a) church
Cornish (Kernewek)	lann [lan:] = yard lannergh = glade
Middle Breton (Brezonec)	lann = moor, heath, moorland lanneg, lannek, lannell = land covered with moor landonenn = swath lann = monastery, church
Breton (Brezhoneg)	lann = moor, heath, moorland lanneg = land covered with moor

Etymology: from the Proto-Indo-European *lendʰ- (land, heath) [source].

Words from the same Proto-Celtic root, via Gaulish and Latin, include lande (moor, moorland, heath) in French, landa (a (sandy) plain) in Spanish, landa (country, field, piece of land) in Basque [source].

The (archaic) English word laund [lɔːnd] (a grassy plain or pasture, especially surround by woodland; a glade) possibly comes from the same Proto-Celtic root, via Middle English, Old French and Gaulish, or from the Proto-Germanic *landą (land), which comes from the same PIE root [Source].

Words from the same PIE roots include land in English, land (land, country) in Dutch, Land (country, state, province, land) in German, land (land, country, nation, state, ground, earth) in Swedish, land (country, land) in Danish, lado (uncultivated, wild land) in Czech, and ледина [ˈlɛdina] (untilled land) in Macedonian [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