Sowilo, meaning "sun", is the reconstructed Proto-Germanic language name of the s-rune (ᛊ, ᛋ). The letter is a direct adoption of Old Italic (Etruscan or Latin) s (𐌔), ultimately from Greek sigma (Σ).
The name is attested for the same rune in all three Rune Poems. It appears as Old Norse and Old Icelandic Sól and as Old English Sigel.
(Lobolyrix)