orb vs crystal ball

orb and crystal ball both are nouns.

Word	Noun	Adjective	Verb	Adverb
orb	Yes	No	Yes	No
crystal ball	Yes	No	No	No

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

orb: an object with a spherical shape
crystal ball: a glass or crystal globe used in crystal gazing by fortunetellers

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

orb (noun)	crystal ball (noun)
the ball-shaped capsule containing the vertebrate eye	a glass or crystal globe used in crystal gazing by fortunetellers
an object with a spherical shape

orb (verb)	crystal ball (verb)
move in an orbit