Eth (/ɛð/ edh, uppercase: ⟨Ð⟩, lowercase: ⟨ð⟩; also spelled edh or eð), known as ðæt (that) in Old English, is a letter used in Old English, Middle English, Icelandic, Faroese (in which it is called edd), and Elfdalian alphabets.
It was also used in Scandinavia during the Middle Ages, but was subsequently replaced with ⟨dh⟩, and later ⟨d⟩.
The Old English Latin alphabet generally consisted of about 24 letters, and was used for writing Old English from the 8th to the 12th centuries. Of these letters, most were directly adopted from the Latin alphabet, two were modified Latin letters (Æ, Ð), and two developed from the runic alphabet (Ƿ, Þ). The letters Q and Z were essentially left unused outside of foreign names from Latin and Greek. The letter J had not yet come into use. The letter K was used by some writers but not by others. W gained usage in late Old English under Norman influence, as seen towards the end of the Peterborough Chronicle manuscript, though in this period W was still a ligature and not a full-fledged letter. The manuscripts MS Harley 208, Stowe MS 57, and Cotton Titus D 18 differ in how they arrange the non-standard Old English letters (Harley has Ƿ–ЖƖÞ, Stowe has Ƿ–ЖÞ, Titus has Ƿ–Þ–Ð), but all three manuscripts place them after the standard Latin letters.