fireball vs doer

fireball and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
fireball	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of fireball; that is, doer is a word with a broader meaning than fireball:

Other hypernyms of fireball include actor, worker.

fireball (noun)	doer (noun)
the luminous center of a nuclear explosion	a person who acts and gets things done
a ball of fire (such as the sun or a ball-shaped discharge of lightning)
a highly energetic and indefatigable person
an especially luminous meteor (sometimes exploding)