self-starter vs fireball

self-starter and fireball both are nouns.

Word	Noun	Adjective	Verb	Adverb
self-starter	Yes	No	No	No
fireball	Yes	No	No	No

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

Other hypernyms of self-starter include ball of fire, human dynamo, powerhouse.

self-starter (noun)	fireball (noun)
an electric starting motor that automatically starts an internal-combustion engine	the luminous center of a nuclear explosion
an energetic person with unusual initiative	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)