artillery vs field gun

artillery and field gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
artillery	Yes	No	No	No
field gun	Yes	No	No	No

As nouns, field gun is a hyponym of artillery; that is, field gun is a word with a more specific, narrower meaning than artillery:

artillery: large but transportable armament
field gun: movable artillery (other than antiaircraft) used by armies in the field (especially for direct support of front-line troops)

Other hyponyms of artillery include cannon, field artillery, four-pounder, depth charge thrower.

artillery (noun)	field gun (noun)
large but transportable armament	movable artillery (other than antiaircraft) used by armies in the field (especially for direct support of front-line troops)
a means of persuading or arguing
an army unit that uses big guns