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 (IPA: [ð]) in the International Phonetic Alphabet. Faroese.
https://en.wikipedia.org/wiki/Eth