en.wikipedia.org/wiki/Thorn_(letter)

Thorn or þorn (Þ, þ) is a letter in the Old English, Old Norse, Old Swedish and modern Icelandic alphabets, as well as modern transliterations of the Gothic alphabet, Middle Scots, and some dialects of Middle English. It was also used in medieval Scandinavia but was later replaced with the digraph th, except in Iceland, where it survives. The letter originated from the rune ᚦ in the Elder Futhark and was called thorn in the Anglo-Saxon and thorn or thurs in the Scandinavian rune poems. It is similar in appearance to the archaic Greek letter sho (ϸ), although the two are historically unrelated. The only language in which þ is currently in use is Icelandic.[1]