Bofors gun vs ack-ack gun

Bofors gun and ack-ack gun both are nouns.

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

As nouns, ack-ack gun is a hypernym of Bofors gun; that is, ack-ack gun is a word with a broader meaning than Bofors gun:

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

Bofors gun (noun)	ack-ack gun (noun)
an automatic double-barreled antiaircraft gun	artillery designed to shoot upward at airplanes