ill-omened vs doomed

ill-omened is not a noun while doomed is a noun.

Word	Noun	Adjective	Verb	Adverb
ill-omened	No	Yes	No	No
doomed	Yes	Yes	No	No

As adjectives, ill-omened and doomed are synonyms defined as:

Other synonyms of ill-omened include ill-fated, ill-starred, unlucky.

ill-omened (noun)	doomed (noun)
	people who are destined to die soon

ill-omened (adjective)	doomed (adjective)
marked by or promising bad fortune	(usually followed by `to') determined by tragic fate
	marked for certain death
	in danger of the eternal punishment of Hell
	marked by or promising bad fortune