OMEN, n. A sign that something will happen if nothing happens.

Source: THE DEVIL'S DICTIONARY ((C)1911 Released April 15 1993)
 

Omen \O"men\, n. [L. omen, the original form being osmen, according to Varro.]

An occurrence supposed to portend, or show the character of, some future event; any indication or action regarded as a foreshowing; a foreboding; a presage; an augury. [1913 Webster]

Bid go with evil omen, and the brand Of infamy upon my name. --Milton. [1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

Omen \O"men\, v. t. [imp. & p. p. Omened; p. pr. & vb. n. Omening.]

To divine or to foreshow by signs or portents; to have omens or premonitions regarding; to predict; to augur; as, to omen ill of an enterprise. [1913 Webster]

The yet unknown verdict, of which, however, all omened the tragical contents. --Sir W. Scott. [1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

90 Moby Thesaurus words for "omen": actuarial prediction, adumbrate, adumbration, apocalypse, augur, augury, auspicate, auspice, betoken, betokening, betokenment, bode, boding, danger sign, early symptom, falling barometer, forebode, foreboding, forecast, forecasting, foreshadow, foreshadowing, foreshow, foreshowing, foresight, foretelling, foretoken, foretokening, forewarning, gathering clouds, guesswork, harbinger, have a hunch, have an intimation, high sign, improbability, indicant, indication, portend, portent, precursor, predict, prediction, prefiguration, prefigurement, prefiguring, preindication, preliminary sign, premonition, premonitory shiver, premonitory sign, premonitory symptom, presage, presaging, presentiment, preshowing, presignifying, probability, prodroma, prodrome, prognosis, prognostic, prognostication, promise, prophecy, prophesying, prospectus, quarantine flag, red flag, red light, shadow, shadow forth, sign, skull and crossbones, soothsay, speculation, statistical prediction, storm petrel, stormy petrel, symptom, thundercloud, thunderhead, token, tokening, type, vaticination, warning sign, warning signal, yellow flag, yellow jack

Source: Moby Thesaurus II by Grady Ward, 1.0
 

omen

Source: WordNet (r) 2.0
 

Omen \O"men\, n. [L. omen, the original form being osmen, according to Varro.]

An occurrence supposed to portend, or show the character of, some future event; any indication or action regarded as a foreshowing; a foreboding; a presage; an augury.

Bid go with evil omen, and the brand Of infamy upon my name. --Milton.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Omen \O"men\, v. t. [imp. & p. p. Omened; p. pr. & vb. n. Omening.]

To divine or to foreshow by signs or portents; to have omens or premonitions regarding; to predict; to augur; as, to omen ill of an enterprise.

The yet unknown verdict, of which, however, all omened the tragical contents. --Sir W. Scott.

Source: Webster's Revised Unabridged Dictionary (1913)