"casual event or occurrence supposed to portend good or evil," 1580s, from Latin omen "foreboding, augury," according to Varro from Old Latin osmen; a word of unknown origin.
"to give indication of the future," 1775, from omen (n.). Related: Omened. The Latin verb ominari meant "to know or tell from omens, to predict."
he looked for an omen before going into battle