Late Middle English; earliest use found in Cursor Mundi: a Northumbrian poem of the 14th century. Either from early Scandinavian (compare Old Icelandic myrkna, Faroese myrkna, Norwegian (Nynorsk) myrkna, Old Swedish myrkna (Swedish mörkna), Danish mørkne (all from the Scandinavian base of Old Icelandic myrkr + the Scandinavian base of Old Icelandic -na)), or from murk + -en, after the early Scandinavian word. In later (Shetland) use from the unattested Norn reflex of the early Scandinavian word represented by the Scandinavian forms listed above.