cannon ball vs round shot

cannon ball and round shot both are nouns.

Word	Noun	Adjective	Verb	Adverb
cannon ball	Yes	No	No	No
round shot	Yes	No	No	No

As nouns, cannon ball and round shot are synonyms defined as:

cannon ball and round shot: a solid projectile that in former times was fired from a cannon

Other synonyms of cannon ball include cannonball.

cannon ball (noun)	round shot (noun)
a solid projectile that in former times was fired from a cannon	a solid projectile that in former times was fired from a cannon