cannonball vs round shot

cannonball and round shot both are nouns.

Word	Noun	Adjective	Verb	Adverb
cannonball	Yes	No	No	No
round shot	Yes	No	No	No

As nouns, cannonball and round shot are synonyms defined as:

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

Other synonyms of cannonball include cannon ball.

cannonball (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