prognostication vs omen

prognostication and omen both are nouns.

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

As nouns, prognostication and omen are synonyms defined as:

Other synonyms of prognostication include portent, presage, prodigy, prognostic.

prognostication (noun)	omen (noun)
knowledge of the future (usually said to be obtained from a divine source)	a sign of something about to happen
a statement made about the future
a sign of something about to happen

prognostication (verb)	omen (verb)
	indicate, as with a sign or an omen