Words for cattle, cow, bull, calf and related things in Celtic languages.

Words marked with a * are reconstructions.

Proto-Celtic	*bāus = cow *bow = cow
Celtiberian	boustom = stable (?)
Old Irish (Goídelc)	bó [boː] = ox, cow
Middle Irish (Gaoidhealg)	bó = ox, cow bóaire = stock-master, stock-owner (“cow-noble”) bólacht = stock of cattle bómlacht = cow’s milk búarach = owner of cows
Irish (Gaeilge)	bó [bˠoː] = cow bó mhara = sea-cow, manatee bó shamhraidh = ladybird bó-aire = cattle lord, cattle owner bódóir = cow-doctor
Scottish Gaelic (Gàidhlig)	bò [boː] = cow bò b(h)ainne = dair/milk cow boineag = small cow bòthach = pertaining to or abounding in cows
Manx (Gaelg)	booa = cow booa vluight = dairy cow boin = very little cow
Proto-Brythonic	*bʉ = cow
Middle Welsh (Kymraec)	buv, bu, buw = cow
Welsh (Cymraeg)	bu = cow, ox, head of cattle (as a standard of value in the Welsh laws) buach = cowherd, rustic, wretched creature biw = cow, cattle, horned cattle
Middle Cornish (Cernewec)	biuh = cow
Cornish (Kernewek)	bu = cow
Breton (Brezhoneg)	bu = cow

Etymology: from the Proto-Indo-European *gʷṓws (cattle). The old Galician word busto (enclosed pasture, a herd of cattle) comes from the same Proto-Celtic roots, via Celtiberian [source].

Proto-Celtic	*boukkā = cow
Proto-Brythonic	*bʉx = cow
Middle Welsh (Kymraec)	buvch, buwch = cow
Welsh (Cymraeg)	buwch [bɨu̯χ / bɪu̯χ] = cow buwch y dwfr = hippopotamus buwch goch Duw = ladybird buwchaidd = cow-like, pertaining to cattle, bovine, uncivilized, stolid buwchan = small cow, young cow, heffer buwchfrechu = to vaccinate (with cowpox) buwchfrechiad = (cowpox) vaccination buwchol = bovine
Old Cornish	buch = cow
Middle Cornish (Cernewec)	beuch, buch, beuh = cow
Cornish (Kernewek)	bugh [biʊx / bɪwh] = cow bugh godra = dairy cow bughik = little cow bughik Dhuw = ladybird bughvowes = cowgirl bughwas = cowboy
Middle Breton (Brezonec)	buch = cow
Breton (Brezhoneg)	buocʼh [ˈbɥoːχ / ˈbyːɔχ] = cow buoc’han = ladybird buoc’hken = cowhide

Etymology: from the Proto-Celtic *bāus (cow), the Proto-Indo-European *gʷṓws (cattle) [source].

Old Irish (Goídelc)	crod = cattle, herds, livestock
Middle Irish (Gaoidhealg)	crod, crud, (c)crodh = cattle, herds, stock, property, wealth crodach = wealth, goods
Irish (Gaeilge)	crodh [ˈkɾˠʊh] = cattle, wealth (in cattle), dowry
Scottish Gaelic (Gàidhlig)	crodh [kroː/krɯj] = cattle

Etymology: possibly from Proto-Indo-European *ḱerdʰ- (file, row, herd) [source]. Words from the same roots include herd in English, Herde (herd, flock) in German and herdhe (nest) in Albanian [source].

Old Irish (Goídelc)	ellach [ˈel͈ax] = good, property, livestock
Middle Irish (Gaoidhealg)	ellach = goods, property, stock, cattle
Irish (Gaeilge)	eallach, eallaighe [ˈal̪ˠəx / ˈal̪ˠa(x)] = chattels, goods, cattle, livestock, poultry
Scottish Gaelic (Gàidhlig)	eallach [jal̪ˠəx] = burden, load, goods, property, cattle, livestock
Manx (Gaelg)	ollagh = bovines, cattle, kine

Etymology: uncertain. Possibly related to sluagh (host, force, army; crowd, multitude, throng) [source].

Proto-Celtic	*tarwos = bull
Gaulish	taruos = bull
Old Irish (Goídelc)	tarb [tarv] = bull
Middle Irish (Gaoidhealg)	tarb = bull
Irish (Gaeilge)	tarbh [ˈt̪ˠaɾˠuː / ˈt̪ˠaɾˠu] = bull tarbhadóir = toreador tarbhán = bull-calf, young bull tarbhánta = bull-like, massive, powerful tarbhántacht = bullishness tarbhghadhar = bulldog
Scottish Gaelic (Gàidhlig)	tarbh [tarav] = bull, Taurus tarbh-chù = bulldog tarbh-nathrach (neimhe) = dragonfly tarbh-thonn = mighty wave tarbhach = like a bull, hefty, chunky tarbhan = small bull tarbhan-dè = butterfly
Manx (Gaelg)	tarroo = bull, Taurus taarroo oaldey = bison, buffalo tarroo-choo = bulldog tarroo-feeaih = stag
Proto-Brythonic	*tarw = bull
Middle Welsh (Kymraec)	tarỼ, tarv = bull
Welsh (Cymraeg)	tarw [ˈtaru / ˈtaːru] = bull, uncastrated male ox, papal bull, Taurus (sign of the zodiac); valiant leader, fierce hero tarw dur = bulldozer tarwgi = bulldog
Old Cornish	tarow = bull
Middle Cornish (Cernewec)	tarow = bull
Cornish (Kernewek)	tarow = bull
Old Breton (Brethonoc)	taruu = bull
Middle Breton (Brezonec)	taru = bull
Breton (Brezhoneg)	tarv [ˈtarw / ˈtɑːro] = bull

Etymology: from the Proto-Indo-European *táwros (wild bull, aurochs), which possibly comes from, or was borrowed into Proto-Semtic as *ṯawr- (bull, ox), from which we get ثَوْر (ṯawr – bull, steer, ox, Taurus) in Arabic [Source].

The Old Irish Irish word for bull was borrowed into Old Norse as tarfr, which became tarvur (bull, Taurus, womanizer) in Faroese, and tarfur (bull) in Icelandic [Source].

Words from the same PIE root include Taurus and steer in English, taureau (bull, Taurus) in French, toro (bull) in Spanish, and touro (bull) in Portuguese [Source].

Proto-Celtic	*laygos / *lāɸigos = calf
Old Irish (Goídelc)	lóeg [l͈oːi̯ɣ] = calf, favourite, darling
Middle Irish (Gaoidhealg)	lóeg = calf, favourite, darling, young deer
Irish (Gaeilge)	lao [l̪ˠeː / l̪ˠiː] = (young) calf laoidín = tiny calf laofheoil = veal
Scottish Gaelic (Gàidhlig)	laogh [l̪ˠɯːɣ] = calf, kid (of deer), fawn, term of endearment for a child laoghach = pertaining to or abounding in calves laoghan = little calf
Manx (Gaelg)	lheiy [ax] = calf
Middle Welsh (Kymraec)	lo, lloe, llo = calf
Welsh (Cymraeg)	llo [ɬoː] = calf, bullock, simpleton, dolt llo(e)aidd = calf-like lloeaf, lloeo, lloea = to calve
Old Cornish	loch = calf
Middle Cornish (Cernewec)	leauh, loch = calf
Cornish (Kernewek)	leugh [løːx / leːx / lɛwh] = calf
Middle Breton (Brezonec)	lue, leuè, leuë = calf
Breton (Brezhoneg)	leue [ˈløː.e / lweː] = calf

Etymology: a diminutuve of the Proto-Indo-European *leh₂p- (cattle) [source].

Irish (Gaeilge)	bearach = heifer, young cow
Scottish Gaelic (Gàidhlig)	biorach [birəx] = a weaned but not fully mature calf or foal (up to 2 years); anti-suckling device, sucking preventer, weaner
Welsh (Cymraeg)	bustach / bustych = bullock, ox, steer (possibly related to the above words)

Etymology: from the Old Irish berach [ˈbʲerax] (pointed, sharp; having pointed ears, horned), from bir (stake, spit, point; spear, spike) & -ach (related to, having, characterised by, prone to) [source].

Proto-Brythonic	*ödjon = ox, bull
Middle Welsh (Kymraec)	eydyon, eidon = ox, steer, bullock
Welsh (Cymraeg)	eidion = domestic male of the bovine family, ox, steer, bullock, neat
Old Cornish	odion = bullock
Middle Cornish (Cernewec)	udzheon, odgan = bullock
Cornish (Kernewek)	ojyon = ox
Middle Breton (Brezonec)	egen, eugen, eugenn = ox, steer, beef
Breton (Brezhoneg)	ejen [ˈeːʒɛn] = ox, steer, beef

Etymology: unknown [source].

Proto-Celtic	*anderā = young woman
Gaulish	anderon = heifer
Old Irish (Goídelc)	ainder [ˈan͈ʲdʲər] = married woman; virgin, maiden
Middle Irish (Gaoidhealg)	ander [ˈæn̠ʲəɾˠ] = girl, maiden, lass; young woman
Irish (Gaeilge)	ainnir [ˈæn̠ʲəɾˠ] = girl, maiden, lass; young woman (poetic); attractive woman
Scottish Gaelic (Gàidhlig)	ainnir [an̠ʲɪrʲ] = maiden, virgin; nymph; marriageable woman; young woman
Middle Welsh (Kymraec)	anneir = heifer
Welsh (Cymraeg)	anner [ˈanɛr] = heifer
Old Cornish	annoer = heifer
Cornish (Kernewek)	annor = heifer
Middle Breton (Brezonec)	annoer, onnoer, ounner, onner = heifer
Breton (Brezhoneg)	annoar [ˈãnwar] = heifer

Etymology: possibly related to Basque andere (lady, woman) [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, An Etymological Dictionary of the Gaelic Language, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionaire Favereau, TermOfis, English – ProtoCeltic WordList (PDF), Etymological Dictionary Of Proto Celtic