ball of fire vs fireball

ball of fire and fireball both are nouns.

Word	Noun	Adjective	Verb	Adverb
ball of fire	Yes	No	No	No
fireball	Yes	No	No	No

As nouns, ball of fire and fireball are synonyms defined as:

Other synonyms of ball of fire include human dynamo, powerhouse.

ball of fire (noun)	fireball (noun)
someone whose career progresses rapidly	the luminous center of a nuclear explosion
a highly energetic and indefatigable person	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)