My brother is on a trip through the Isles, staying on Barra at the moment, and posted on Facebook that they were very near to Traigh Mhor (‘Big Beach’), which doubles as the island’s airport.
I saw this & immediately replied Traeth Mawr, so now he’s come back with “…and in Manx or Cornish?”
Help appreciated!
Yn Kernewek (Cornish): Treth Meur! 
(The “eu” is pronounced pretty much as in French fleur.)
I love finding cognates between the different Celtic languages — fairly easy between Welsh, Cornish and Breton, but even more interesting when there are Gaelic ones as well.
In Irish it’s Trá Mhór. A semi-educated guess says it’s Traie Mooar in Manx, but there can be a tendency to look for the familiar when translating. ‘Traie’ mightn’t be used as much in Manx as ‘Trá’ is in Irish. In addition, I have no idea whether there’s a mutation whereby ‘Mooar’ becomes ‘Vooar’.
Now does anyone have the Breton, for a likely 6-way Celtic cognate fest (doesn’t happen often)? 
I got as far as Treizhen (or something like that), but it was only by using Wiktionary. But I think it might actually work all six ways 
I’ve got traezh, which sounds likely (th in Cornish and Welsh usually becomes zh in Breton) — that’s “beach”, according to one online dictionary I managed to find, while traezhen is “sandy shore”. (We have a cognate in Cornish, trethen, which means “sandy patch”.) According to another online dictionary, it looks like meur is the same in both languages, but I’m not sure yet…
And now I’ve had the thought to simply look in An Gerlyver Meur, the largest Cornish dictionary so far published, which has the Breton and Welsh cognates listed under every word that has them. Yes, it’s definitely Traezh Meur in Breton! (I don’t think it would mutate to veur in this case, as traezh is masculine.) So it does work all six ways!