1580s, perhaps via Middle French épique or directly from Latin epicus, from Greek epikos, from epos "word, story, poem," from PIE *wekw- "to speak" (see voice). Extended sense of "grand, heroic" first recorded in English 1731. The noun meaning "an epic poem" is first recorded 1706.
A long narrative poem written in elevated style, in which heroes of great historical or legendary importance perform valorous deeds. The setting is vast in scope, covering great nations, the world, or the universe, and the action is important to the history of a nation or people. The Iliad, the Odyssey, and the Aeneid are some great epics from world literature, and two great epics in English are Beowulf and Paradise Lost.
Note: Figuratively, any task of great magnitude may be called “epic,” as in an “epic feat” or an “epic undertaking.”