This is the stupidest folk etymology I’ve seen in a while:
The word “rune,” as far as I know, comes from the word “runner” where a runner would run with a rune stone four miles down the road, and then he’d give it to another runner, who’d run another four miles to another runner, who’d run another four miles to give it to the King, and the King would read the symbol on the stone and say, “Oh, there’s a wedding in three days.” So that’s how they communicated way back then.
The Oxford English Dictionary has a more reliable etymology:
In origin the same word as ROUN, mystery, etc., but in sense 1 adopted in the 17th cent. (through Danish writers on Northern antiquities) from Old Norse and Icelandic rún, pl. rúnar, later rúnir (Danish rune, pl. runer; Swedish runa, pl. runor). Hence also German and Dutch rune, pl. runen, French rune, pl. runes, etc. In sense 2 the immediate source is the Finnish runo, itself an adoption of the Old Norse word.
Roun, pointed to in the first line of the OED ety, is given this as its origins:
Common Teutonic: Old English rún str. fem., = Middle Dutch rune, ruun (ruen), whisper, secret counsel, etc., Old Swedish rûna (Middle Late German rûne, rûn), Old High German rûna (Middle High German rûne, German raun, dialect rûn), Old Norse rún, Gothic rûna.
There’s also a string of Greek that I don’t have the time to render here.