Letter of the Latin alphabet; used in Icelandic, Faroese, and Old English
Eth ( edh, uppercase: Ð, lowercase: ð; also spelled edh or eð), known as ðæt in Old English, is a letter used in Old English, Middle English, Icelandic, Faroese (in which it is called edd), and Elfdalian. . It was also used in Scandinavia during the Middle Ages, but was subsequently replaced with ⟨dh⟩, and later ⟨d⟩. . It is often transliterated as ⟨d⟩. . The lowercase version has been adopted to represent a voiced dental fricative in the International Phonetic Alphabet. Faroese.
https://en.wikipedia.org/wiki/Eth