orb vs fireball

orb and fireball both are nouns.

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

As nouns, fireball is a hyponym of orb; that is, fireball is a word with a more specific, narrower meaning than orb:

Other hyponyms of orb include crystal ball, camphor ball, mothball, time-ball, globule, spherule, pellet, bolus.

orb (noun)	fireball (noun)
the ball-shaped capsule containing the vertebrate eye	the luminous center of a nuclear explosion
an object with a spherical shape	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)

orb (verb)	fireball (verb)
move in an orbit