Bren gun vs submachine gun

Bren gun and submachine gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
Bren gun	Yes	No	No	No
submachine gun	Yes	No	No	No

As nouns, submachine gun is a hypernym of Bren gun; that is, submachine gun is a word with a broader meaning than Bren gun:

Bren gun: a submachine gun operated by gas pressure; used by the British in World War II
submachine gun: machine gun that is a portable automatic firearm

Bren gun (noun)	submachine gun (noun)
a submachine gun operated by gas pressure; used by the British in World War II	machine gun that is a portable automatic firearm