cannon ball vs cannonball

cannon ball and cannonball both are nouns.

Word	Noun	Adjective	Verb	Adverb
cannon ball	Yes	No	No	No
cannonball	Yes	No	No	No

As nouns, cannon ball and cannonball are synonyms defined as:

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

Other synonyms of cannon ball include round shot.

cannon ball (noun)	cannonball (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