Omen, n.
Etymology: [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.
1 other Webster entry under this spelling
Omen, 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.
Shades of meaning
Fernald has no entry of its own for omen; he lists it under sign.
He lists it without comment; the entries above explain its neighbors.
Antonyms
none given