four-pounder vs ordnance

four-pounder and ordnance both are nouns.

Word	Noun	Adjective	Verb	Adverb
four-pounder	Yes	No	No	No
ordnance	Yes	No	No	No

As nouns, ordnance is a hypernym of four-pounder; that is, ordnance is a word with a broader meaning than four-pounder:

Other hypernyms of four-pounder include artillery, gun, heavy weapon.

four-pounder (noun)	ordnance (noun)
an artillery gun that throws a shot weighing four pounds	military supplies
	large but transportable armament