Many varying etymologies of Yr Wyddfa ("Snowdon") and Eryri ("Snowdonia" - itself a faux-Latin Victorian coinage) floating about here. So! here's the most definitive explanation I can muster for the origins of the Cymraeg names: (1/x)

Wyddfa is from gwydd + ma, where gwydd is 'sight, face' which therefore likely signified a visible peak; ma (mutating to fa) is 'place', so = the "(high and) visible place" perhaps. (2/x)

Gwydd does also mean a grave or barrow or cairn, but this may be a later meaning retrospectively applied to Yr Wyddfa. The link with Rhita Gawr is of course a legend, and it's likely the mountain name predates this link. (3/x)

Eryri isn't from eryr 'eagle' nor is it a Latin borrowing, but most likely a form of a Celtic root ~*ar- referring to a ridge/edge (the nearby ridge called Aran is of the same origin)... (4/x)

...though the Welsh word for eagle is also probably derived from that root separately (they are both high-up things!). Eryri is plural so "ridges". (5/x)

Like Rhiannon Coslett writes in this great article in The Guardian today, language is political; I'd say names are doubly so. There's also a lot of romance and identity attached to names that enrich etymologies. (6/x) https://www.theguardian.com/commentisfree/2021/apr/30/snowdon-yr-wyddfa-language-political-english-wales-ireland

Above I gave the (I think) linguistically most plausible origins for Wyddfa and Eryri. As a linguist I encourage people to remember that most words have mundane roots. But the links to eagles and giants and cairns and invaders are part of these words' histories too. (7/x)

When something has been around as long as a mountain (& longer than any humans who laid eyes on it) I think it deserves respect when naming it. Wyddfa probably wasn't the first name given to it, but it's likely the earliest we know of, and I think that counts for something. (Fin)

O.N. Ymddiheuriadau am yr edefyn Saesneg gyda llaw. Eisiau sicrhau bod y 'neges' yn cyrraedd tu hwnt i'r gororau (NB mae 'goror' < gor- + ôr, a'r ail elfen yn debygol o'r un gwraidd ac Eryri!).