In general, in the Celtic words, be it noted, mh and bh are the sound we call v; ch is breathed, if possible, as in familiar loch, a word for lake (but k will do); -gach has often by our day gone to the sound of a hard -gy; and the profusion of vowels has generally a single simple sound at the heart.
In the Welsh most notably -dd- is -th-.
In the English, easiest to render ae- as simple e-, and to treat hr- as r-.
Where a name has a more familiar form, it will be given in capitals.
And if for any reader this small list provokes further curiosity, Celtic, Welsh, and old English reference works are not that difficult to find. A good place to begin is, after all, with names, the -nesses and -hams and -denes and -eys that come off modern tongues as if they had no meaning in themselves. Names do have power, after all, that of conjuring images of places we have not seen.
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Lexicon
aelf(elf) OE an elf
Aelfraeda(elf red a) OE from aelf [elf] and raeda [counsel]
aesc(esh) OE ash
Aescbourne(esh burn) OE ash brook: ASHBURN
Aescford(esh ford) OE ash ford: ASHFORD
Aesclinn(esh linn) OE ash pooclass="underline" ASHLIN
Airgiod(ar gi ud) C silver
An Beag(an beg) C small
Aodhan(a o dan) C rascal
ap(ap) W son of
Arafel(ar a fel) C from AOIBHEIL (a o ev al) joyous
Ban(ban) C fair, pale
Banain(ban en) C fair; BANNEN
Bebhinn(bev in) C BEVIN
Beorc(burk) OE birch: BURKE
Beorhthramm(burt ram) OE: bright raven; BERTRAM
Boglach(bog lach) C marsh
bourne(burn) OE stream
brad(brad) OE broad
Bradhaeth(brad heath) OE broad heath
Branwyn(bran win) W from BRONWEN (bron win) white breast
Cadawg(ca-doc) W warrior; CADDOCK
Cadhla(ca ly) C fighter; CALEY
caer(ker) W stronghold
Caer Damh(ker dav) C stag keep
Caer Luel(ker lel) OE castle keep: CARLISLE
Caer Wiell(ker well) OE spring keep
Caerbourne(ker burn) castle brook
Caoimhin(ku EV in) C kindly: KEVIN
Carraig(KAR rak) C standing stone
Caerbhallain(KER va len) C victor: CARROL (an)
Ciaran(KEE ran) C twilight: KIERAN
Cinhil(kin il)
Cinnfhail(kin vel) C head
Coinneach(ko en nach) C moss: KENNETH
Conmhaighe(kon vay) C hound: CONWAY
Cuilean(kul an) C cub: QUILLAN
Dalach(da loch) C advisers DALEY
damh(dav) C stag
Daoine Sidhe(thee na Shee) C the People of Peace; the folk of Faery. Often powers felt to be dangerous and perhaps ill-wishing are named by names felt to be quite contrary to their natures, to avoid calling them up accidentally or offending them by mentioning their true names; again, the feeling is that the true name is not for using. And of course the Daoine Sidhe are not likely to give the true name of all their kind for common use. Other names are the FAIR FOLK, for much the same reason. SIDHE applies to many kinds of creature: the Gruagach by some extension is one of the Sidhe and so are some things very much worse to look on. But the Daoine Sidhe are the highest of their kind.
Diarmaid(der mit) C free: DERMOT
Diomasach(dem sey) C proud: DEMPSEY
Donn(don) C brown
Donnchadh(don cad) C brown tartan: DUNCAN
Dryw(drew) W sight: DREW
Dubh(du) C black
Dubhlachen(du la han) C dark; DOOLAHAN
Dun na h-Eoin(dun na hey win) C tower of birds
each(ek) C horse
Eachthighern(ek ti arn) C lord of horses
ead(ed) OE noble
eald(eld) OE old
Evald(ev ald) OE fr. AECWEALD, oak wood
Fearghal(fir gal) C valorous man: FARREL
Feochadan(fo ka dan) C thistle
Fionn(fee an) C fair: FINN
Fionnbharr(fin var) C fairhair
Fionnghuala(fin el a) C white shoulder: FINELLA
Fitheach(fay ak) C raven
Flann(flan) C red
Glas(glass) C gray
Gruagach(gru gy) fr. C: hairy. The word has scattered meanings. As one of the Sidhe, this is one of the working sort who performs homely tasks.
Haesel(hay sel) OE hazeclass="underline" HAZEL
haeth(heath) OE heath: HEATH
Holen(ho len) OE holly: HOLLIN
Hrothhramm(roth ram) OE famous raven
Laochailan(la ok lan) C hero: LACHLANN
linn(lin) OE pooclass="underline" LYNN
lios(li-ess) C Sidhe fort
Liosliath(liess-lia) C gray Sidhe fortress: LESLEY
Lioslinn(liess-lin) C Sidhe fort lake
Lonn(lon) C strong; LONN
Meara(mer a) C wild laughter
Meredydd(me re dith) W sea: MEREDITH
Muirne(murn a) C hospitality; MYRNA
Niall(ne al) C hero: NEAL
Ogan(o gan) C youth
righ(ree) C king
ruadh(ro ak) C red; red deer
Ruaidhrigh(ru a ree) C red king or deer king; RORY
Sgeulaiche(skel ly) C storyteller; SKELLY; SCULLY
Siobrach(sov rak) C primrose
Siolta(shel ta) C waterfowl
Skaga(skag a) C stand of trees; SHAW
Taithleach(tul ly) C experienced; TULLY
Tiamhaidh(tiv ak) C drear
tighearn(ti am) C lord
wiell(well) OE spring
wulf(wolf) OE wolf