Eth, known as ðæt in Old English, is a letter used in Old English, Middle English, Icelandic, Faroese, and Elfdalian. Wikipedia

A letter of the Latin alphabet Wikipedia Disambiguation

A letter used in Old English, Icelandic, Faroese and Elfdalian Wikipedia Disambiguation

Three different letters Wikidata

A letter (capital Ð, small ð) introduced into Old English to represent its dental fricative, then not distinguished from the letter thorn, no longer used in English but still in modern use in Icelandic, the IPA and other phonetic alphabets to represent the voiced dental fricative "th" sound as in the English word then. The letter is also used in Faroese, but is generally silent in that language. Wiktionary

Letter. Wiktionary (translation)