prognosticate vs omen

prognosticate is not a noun while omen is a noun.

Word	Noun	Adjective	Verb	Adverb
prognosticate	No	No	Yes	No
omen	Yes	No	Yes	No

As verbs, prognosticate and omen are synonyms defined as:

Other synonyms of prognosticate include augur, auspicate, betoken, bode, forecast, foreshadow, foretell, portend, predict, prefigure, presage.

prognosticate (noun)	omen (noun)
	a sign of something about to happen

prognosticate (verb)	omen (verb)
make a prediction about; tell in advance	indicate, as with a sign or an omen
indicate, as with a sign or an omen