From today’s Corrections and clarifications in The Guardian:
It is tautologous to refer to “Mount Snowdon” as we did in panel text (Snowdon strike, 30 July, page 18). The English name Snowdon is derived from the Old English snaw dun meaning “snow hill”; in Welsh the peak is Yr Wyddfa.
I didn’t know what “tautologous” meant, so I looked it up:
the saying of the same thing twice in different words, generally considered to be a fault of style (e.g., they arrived one after the other in succession).
So “Mount Snowdon” is tautologous because it’s saying, in essence, “Mount Snow Mount.”
As it happens, Olivia and I were searching for just that word earlier in the year when discussing phrases like “PIN number” and “ATM machine.”