Words for cheese and related words in Celtic languages.

Old Irish (Goídelc)	cáise = cheese
Irish (Gaeilge)	cáis [kɑːʃ / kæːʃ] = cheese cáiseoir = cheese-maker, cheese-monger cáisiúil = cheesy
Scottish Gaelic (Gàidhlig)	càise [kaːʃə] = cheese càisean, cùl-càise = cheese rind brèid-càise, anart-càise = cheesecloth
Manx (Gaelg)	caashey = cheese, cheesy caasheydagh = cheesy
Proto-Brythonic	*kọs = cheese
Middle Welsh (Kymraec)	caws, caus = cheese
Welsh (Cymraeg)	caws [kau̯s] = cheese, curds, a cheese cawsa = to beg cheese, collect cheese cawsai = cheese begger, one who makes cheese cawsaidd = caseous, cheesy cawsion = curd, curds, curdlings cawslestr = cheesel, cheese vat/mould cawslïain = cheese-cloth cawsty = cheese house, dairy cosyn [ˈkɔsɨ̞n / ˈkɔsɪn] = a piece of cheese
Cornish (Kernewek)	keus [køːs] = cheese keuswask = cheese press
Breton (Brezhoneg)	keuz = cheese keuzerezh = cheese factory

Etymology: from the Latin cāseus (cheese), from the Proto-Indo-European *kwh₂et- (to ferment, become sour) [source].

Middle Breton)	fourondec, foulondec = cheese
Breton (Brezhoneg)	formaj = cheese fourmajerezh = cheese factory

Etymology: from the Latin Latin fōrmāticum (cheese), short for cāseus fōrmāticus (form cheese), from cāseus (cheese) amd fōrma (form, mold) [source]. More cheesy words in European languages.

Words marked with a * are reconstructions.

Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, eDIL – Electronic Dictionary of the Irish Language, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionaire Favereau, TermOfis