In this post we’re looking at words for fast(ing), abstinence, Friday and related things in Celtic languages.

Words marked with a * are reconstructions.

Old Irish (Goídelc)	aín(e) [ˈaːi̯nʲ] = fast, fasting (period of time when one abstains from or eats very little food) aínid = to fast Cétaín [ˈkʲeː.d̪aːi̯nʲ] = Wednesday (“first fast”) Dardóin [d̪aɾˈd̪aːi̯nʲ] = Thursday (a contraction of etar-dá-óin – “between two fasts”) aín dídine, oín dídine = Friday (“last fast”)
Middle Irish (Gaoidhealg)	aín = fast, period of fasting aínid = to fast, to keep a fast aíntech = abstemious, ascetic cétaín(e), cetain, cétain [ˈkʲeː.d̪aːi̯nʲ] = Wednesday dardoín, dardáin, dardain = Thursday aín dídin(e), aín díden = Friday
Irish (Gaeilge)	aoine [ˈiːnʲə] = fast, fasting, abstinence (archaic), Friday aointeach = falling on / pertaining to Friday (Dé) Céadaoin [(dʲeː) ˈceːd̪ˠiːnʲ] = (on) Wednesday Déardaoin [ˌdʲeːɾˠˈd̪ˠiːnʲ / dʲaɾˠˈd̪ˠiːnʲ] = (on) Thursday Dé hAoine [dʲeː ˈhiːnʲə / dʲaˈhiːnʲə] = (on) Friday Aoine an Chéasta = Good Friday
Scottish Gaelic (Gàidhlig)	aoine [ɯːn̪ʲə] = Friday, fast, fast-day aoineach [ɯːn̪ʲəx] = fasting, fast DiCiadain [dʲɪˈkʲiədɪn̪ʲ] = Wednesday DiDaoirne [dʲɪˈdɯːr̪n̪ʲə] = Thursday DihAoine [dʲɪˈhɯːn̪ʲə] = Friday
Manx (Gaelg)	Yn Eney [tʃeu] = Friday Jeheiney [dʒeˈhəːnʲə] = (on) Friday Jardain, Jerdein = (on) Thursday Jecrean, Crean, Curain = (on) Wednesday
Middle Welsh (Kymraec)	unpryt, vnpryd, vn pryt, ympryt, umpryt = a fast(ing), hunger strike ym prydant, vn prydyaf, vmprydio = to fast, to be or go on hunger strike, to keep (a fast) unprydyawl, ymprydiol, vnprytiol = pertaining to a fast or fasting, hungry
Welsh (Cymraeg)	ympryd, umpryd, unpryd, un pryd [ˈəmprɨ̞d / ˈəmprɪd] = a fast(ing), hunger strike ymprydiaeth = a fast(ing) ympryd(i)o = to fast, to be or go on hunger strike, to keep (a fast) ymprydiol, unprydiol = pertaining to a fast or fasting, hungry ymprydiwr = one who fasts, faster
Middle Breton (Brezonec)	yeun, iun, iunou, yun, jun = fasting yunaff = to fast
Breton (Brezhoneg)	yun [jỹːn] = fasting yunadenn = a period of fasting yunan, yunañ, yuniñ [ˈjỹː.nã / ˈjỹː.nĩ] = to fast yuner / yunerez [ˈjỹː.nɛr / jy.ˈneː.res] = fasting person, hunger strike

Etymology: from Latin ieiūnium (fast [day], fasting, Lent, hunger), from ieiūnus (fasting, abstinent, hungry), Proto-Italic *jagjūnos, from Proto-Indo-European *h₁yaǵ-yu-s, from *h₁yaǵ- (to sacrifice, worship) [source].

Words from the same roots include dinner and jentacular (pertaining to breakfast) in English, xantar (dinner, lunch) in Galician, yantar (to lunch, dine, eat) in Spanish, άγιος (ágios – holy, saintly, Saint) in Greek, and جشن (jašn – celebration, festival, feast) in Persian [source].

Old Irish (Goídelc)	troscad, troscud = (coercive) fasting
Middle Irish (Gaoidhealg)	troscad, troscud = (act of) fasting troiscid, troscaid, troscad = to fast
Irish (Gaeilge)	troisc [t̪ˠɾˠɔsˠk] = fast troscach = fasting troscadh [ˈt̪ˠɾˠosˠkə / ˈt̪ˠɾˠʌsˠkə] = to fast, fasting
Scottish Gaelic (Gàidhlig)	trasg [trasg] = fasting, fasting, diet, dieting traisg = to fast, diet là-trasgaidh = fast-day
Manx (Gaelg)	trostey = fasting brishey trostey = breakfast

Etymology: from Latin ieiūnium (fast [day], fasting, Lent, hunger), from ieiūnus (fasting, abstinent, hungry), Proto-Italic *jagjūnos, from Proto-Indo-European *h₁yaǵ-yu-s, from *h₁yaǵ- (to sacrifice, worship) [source].

Middle Welsh (Kymraec)	dyrwest, dyruest, dyrỽe(i)st = abstinence from food and drink, fasting, fast dyrwestu, dyrwest = to fast, to abstain from food and drink dir westua, dyrwestfa = fast, abstention, a fasting, penitence
Welsh (Cymraeg)	dirwest, dyrwest [ˈdɪrwɛst] = abstinence from food and drink, fasting, fast, temperance, self-restraint, teetotalism, abstemious, sober, chaste, continent dirwestaf, dirwest(u) = to fast, to abstain from food and drink dirwestfa [dɪrˈwɛstva] = fast, abstention, a fasting, penitence dirwestol [dɪrˈwɛstɔl] = abstinent from alcohol, abstemious

Etymology: unknown [source].

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, Dictionaire Favereau, TermOfis, English – ProtoCeltic WordList (PDF), Etymological Dictionary Of Proto Celtic