pom-pom vs ack-ack gun

pom-pom and ack-ack gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
pom-pom	Yes	No	No	No
ack-ack gun	Yes	No	No	No

As nouns, pom-pom and ack-ack gun are synonyms defined as:

pom-pom and ack-ack gun: artillery designed to shoot upward at airplanes

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

pom-pom (noun)	ack-ack gun (noun)
artillery designed to shoot upward at airplanes	artillery designed to shoot upward at airplanes
decoration consisting of a ball of tufted wool or silk; usually worn on a hat