What really links place names in Brittany, Cornwall and Wales (apart from a few hundred Celtic saints)?

Place Name Elements in Breton, Welsh and Cornish (with examples and English gloss)

BRETON	CORNISH	WELSH	ENGLISH	EXAMPLES C=Cornwall; W= Wales
aut, alt, aod	alt, als, aulz	allt	hill, slope, cliff	Duault (22), Nansalsa (C), Allt-golau (W)
ael	ael	ael	summit, brow, ridge	Hirael (35), Aelbryn (W)
aval	aval, avallen	afal, afallen	apple	Availles-sur-Seiche (35), Rosevallen (C), Dolafallen (W)
aon, aven	auon, awan	afon	river	Pont-Aven (29); Arrowan (C), Aberavon (W)
arcae	-	argae	dam, embankment	Erquy (22), Argae Alwen (W)
ard, art, arz	are, ard, arth	ardd	hill, elevation	Arzon (56); Trenarth (C), Pennard (W)
arz, arzh	art, arth	arth	bear	Île-d'Arz (56), Carn Arthen (C), Aber-arth (W)
ascorn	-	asgwrn, esgyrn	bone/s	Coatascorn (22), Esgyrn (W)
banadl	banollack	Banadl(og)	broom (patch)	Plobannalec (56), Bonallack (C), Cefn Banadl (W)
bed, bez	beth	bedd	grave	Rospez (22), Trembethow (C), Beddgelert (W)
beduan	bedou, besow	Bedw(en)	birch tree/grove	Bédée (35), Lambessow (C), Bedwlwyn (W)
bihan	By(gh)an, bean	bychan	small, little	Henanbihan (22), Carn Bean (C), Morfa Bychan (W)
bot, bod	Bod, bos	bod	dwelling/home	Botmeur (29), Boslowick (C), Bodrhychwyn (W)
bre	bre(a)	bre	hill(ock)	Brélès (29), Brea (C), Pen-bre (W)
brec’h, brith	brech, bregh, brith	brych	mottled/hilly place	Trébry (22), Trebrith (Cornwall), Brechfa (W)
bran, brain	brane	brân, brain	crow(s)	La Chapelle-de-Brain (35), Brane (C), Cwm-Brân (W)
broenn	Bronnen, brunnen	brwyn(en)	rushes/marsh shrubs	Broons (22), Brunnion (C), Cwmbrwyn (W)
caer, kaer, kêr	caer, car, kear	caer	fort, enclosure, village	Kerbors, Caervallack (C), Caernarfon (W)
cam, kamm	cam, cabm	cam	curved/crooked	Camlez (22), Cambeak (C), Camros (W)
carn/karn	carn/kern	carn	cairn, tor, crag	Carnac (56), Carn Brea (C), Talygarn (W)
caro, karo	caruu, carow	carw	stag (red deer)	Caro (56), Lancarrow (C), Cilcarw (W)
castell, kastell	castell	castell	castle	Trégastel (22), Castallack (C), Trecastell (W)
coët, c/koad,	cuit, coys, cooz	coed	wood, forest	Plancoët (22), Pencoys (C), Bettws-y-coed
croes, kroaz	crois, crows/z	crwys, croes	cross	Plougras (22), Crows-an-wra (C), Bryncroes (W)
crug, krug	cruc/k, creeg	crug	mound, tumulus, barrow	Cruguel (22), Crugillick (C), Bryncrug (W)
cum/com	coombe, cum,	cwm	valley, dale	Commana (29), Coombe (C), Cwm-barre (W)
din	din, dun, dinas	din	hill fort	Dinan (22), Castle an Dinas (C),  Dinas Mawddwy (W)
dol	dol	dol	River meadow	Dol-de-Bretagne (35), Godolphin (C), Dol-y-bont (W)
dour	douer	dwfr, dwr	water, river	Pouldouran (22), Dowran (C), Cwmdwr
drein, draenen	drein	draen, drein	thorn (bushes)	Rostrenen (22), Draynes (C), Bryndreiniog (W)
drez	dreis/z	drys	brambles	Trédrez (22), Poltrease (C), Dryslwyn (W)
du	duw, du(e)	du	dark, black	Duault (22), Toldhu (C), Ynys-ddu (W)
enez	ennis, enys	ynys	island, remote place	Douarnenez (29),   Ynys Môn (W), Bosporthennis (C),
Ethin(oc)	eithin	Eithin(og)	gorse	Plouhinec (29, 56), Rosenithon (C), Bryn Eithinog (W)
faou	faw	ffaw	beech	Le Faouët (22, 56), Fowey (C), Ffawyddog (W)
garu	garow	garw	rough, hard, rugged	Garlan (29), Garrow Tor (C), Blaengarw (W)
glas	glaze	glas	grey, green, blue	Kerglas (29), Glasney (C), Bryn Glas (W)
geun, goen	goen, goon	gwaun	downs, moorland	Tréguennec (29), Goonlaze (C), Abergwaun (W)
goulou, golou	golow, gulow	golau	bright, light	Bringolo (22), Tregullow (C), Allt-golay (W)
guar	gwar	gwar	upper	Le Gouray (22), Porthgwarra, Gwarallt (W)
guen, gwenn	guen, gwyn	gwyn	white, fair, sacred	Guenroc (22), Gwendreath (C), Bron-gwyn (W)
gwern, guern	gwearn	gwern	(alder tree) swamp	Le Guerno (56), Penwarne (C), Pengwern (W)
heli, hili	heyl, hayl	heli	brine, salting(s)	Hillion (22), Hayle (C), Pwllheli (W)
hen	hen	hen	old	Henvic (29), Hendra (C), Henllan (W)
hanveg, havreg	havar, havosow	hafod	fallow, summer pasture/residence	Hanvec (29), Halvosso (C), Hafoty (W)
hir	hir, heer, hyr	hir	long, tall	Hirael (35), Hyrlas (C), Pont-hir (W)
ilis/z	eglos	eglwys	church	Bodilis (29), Lanteglos (C), Trefeglwys (W)
iurgch	iorgh, yorth, yorch	iwrch	roebuck	Le Yuch (29), Carnyorth (C), Pwlliwrch (W)
killi	kelli, kelly, killy	celli	grove	Penguily (22), Kelly (C), Pencelli (W)
lann	lan	llan	church site, monastery	Lancieux (22), Landewednack (C), Llanelli (W)
lec’h	legh, leh	llech	slab, stone ledge	Ploulec’h (22), Treleigh (C), Harlech (W)
lis, lez	les, lys, lis	llys	court, hall	Lezardrieux (22), Lesnewth (C), Llysfaen (W)
l(a)ouen, levenez	louen, lowen	lleuen, llawen	happy	Poullaouen (29), Trelawne (C), Bodlawen (W)
loc	loc, lok	lloc	chapel, cell, holy place, enclosure	Locronan (29), Luxulyan (C),  Lloc (W),
loc’h, louc’h, loc	loch, logh, loe	llwch	lake, inlet, pool	Loudéac (22), Looe (C), Amllwch
lost	lost	llost	tail, end	Loscouët-sur-Meu (22), Lostwithiel (C)
maen, main	main, men	maen	stone	Tramain (22), Tramaine (C), Llechfaen (W)
manac’h, menec’h	manach	mynach, menych	monk(s)	Gommenec’h (22), Manaccan (C),  Ystradmynach (W)
marc’h	march, marth	march, meirch	horse	Penmarch (29), Penmarth (C), Rhos-meirch (W)
meillon, melchon	mellyon, mellian	meillion	clover	Mellionec (22), Rosemullion Head (C), : Cwm Meillionen (W)
meur	maur, mere	mawr	big, great	Botmeur (22), Porthmeor (C), Llanbadarn Fawr (W)
menez (méné)	menit, meneth, mena	mynydd	hill, mountain	Plounéour-Ménez (29), Menacuddle (C), Mynydd Isa (W)
moel, mel, moal	moyl, mol, moel	moel	bare hill	Kergrist-Moëlou (22), Molinnis (C), Nant-y-moel (W)
mor	mor	mor	sea	Côtes d’Armor (22), Morvah (C), Brynmôr (W)
moc’h	mogh	moch	pig	Mohon (56), Tremough (C), Crug-moch (W),
nant/ant	nant/nans	nant	valley	Fouesnant (29), Trenant (C),
nowid, nevez	newyth, noweth	newydd	new	Plounévez-Moëdec (22), Trenoweth (C), Casnewydd (W)
onn	onnen, en	onnen, onn	ash (tree)	Henon (22), River Inny (C), Trefonnen (W)
pen(n)	pen	pen	head, top, end	Pencran (29), Penzance (C), Penrhyncoch (W)
perth	perth	perth	bush, hedge, thicket	Le Pertre (35), Penberth (C), Berth-ddu (W)
ple, pleu, plou, plu	plu	plwyf	parish	Ploumeur (29), Pelynt/Plunent (C), Blaen-plwyf (W)
pont	pons/pont	pont	bridge	Hennebont (56), Ponshallow (C), Pen-y-bont (W)
porth, porzh, pors	porth, por	porth	cove, harbour, gateway	Porspoder (29), Porthgwarra (C), Portcawl (W)
poul(l), pol	pol	pwll	pool, creek, cove	Pouldouran (29), Polkanuggo (C), Pwyllgwrach (W)
reden, raden	redan, reden	rhedyn	bracken, fern	Radenac (56), Splattenridden (C), Rhedyn-coch (W)
ret, red, re	rit, res	rhyd	ford	Perret (22), Redruth (C), Penrhyd (W)
ros, roz	ros, rose	rhos	promontory, coastal slope	Roscoff (29), Penrose (C), Rhosllanerchrugog (W)
saozneg, saoson	sawsen	saesneg, saeson	Saxon, English(man)	Sauzon (56), Carsawsen (C), Nant-y-saeson
skaw(ieg)	scaw(en)	ysgeifiog	(place with) elder trees	Squiffiec (22), Boscawen (C), Tresco (Scilly Is.), Ysgeifiog (W)
ti/ty	ti/chy	tŷ	house, cottage	Le Croisty (56), Chysauster (C), Ty-groes (W)
tre, trev, tref	tre(a), tref	tre, tref, trev	farm, settlement, village	Trégueux (22), Tregony (C), Treforest (W)
treizh, traez, trez	treath	traeth	beach, sand	Plounéour-Trez (29), Portreath (C), Trefdraeth (W)
uchel, uhel, huel	(h)uhel, ughell	uchel	high	Huelgoat (29), Trewhella (C), Bonuchel (W)