Dictionary.net

• rag'na-r[=oo]k', n. the end of the world when the gods (Odin, Thor, &c.) shall be overcome by their enemies and the world burnt up. [Ice. ragna rökr, twilight of the gods--rögn, régin, the gods, rökr, darkness; but orig. ragna rök, the history of the gods--rök, reason, judgment.]

1908 - Chambers's Twentieth Century Dictionary of the English Language
By Thomas Davidson