antiaircraft vs flack

antiaircraft and flack both are nouns.

Word	Noun	Adjective	Verb	Adverb
antiaircraft	Yes	Yes	No	No
flack	Yes	No	No	No

As nouns, antiaircraft and flack are synonyms defined as:

Other synonyms of antiaircraft include ack-ack, ack-ack gun, antiaircraft gun, flak, pom-pom.

antiaircraft (noun)	flack (noun)
artillery designed to shoot upward at airplanes	artillery designed to shoot upward at airplanes
	intense adverse criticism
	a slick spokesperson who can turn any criticism to the advantage of their employer

antiaircraft (adjective)	flack (adjective)
designed for defense from a surface position against air attack