breech vs rear of tube

breech and rear of tube both are nouns.

Word	Noun	Adjective	Verb	Adverb
breech	Yes	No	No	No
rear of tube	Yes	No	No	No

As nouns, breech and rear of tube are synonyms defined as:

breech and rear of tube: opening in the rear of the barrel of a gun where bullets can be loaded

Other synonyms of breech include rear of barrel.

breech (noun)	rear of tube (noun)
opening in the rear of the barrel of a gun where bullets can be loaded	opening in the rear of the barrel of a gun where bullets can be loaded