Bren vs Bren gun

Bren and Bren gun both are nouns.

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

As nouns, Bren and Bren gun are synonyms defined as:

Bren and Bren gun: a submachine gun operated by gas pressure; used by the British in World War II

Bren (noun)	Bren gun (noun)
a submachine gun operated by gas pressure; used by the British in World War II	a submachine gun operated by gas pressure; used by the British in World War II