crystal ball vs orb

crystal ball and orb both are nouns.

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

As nouns, orb is a hypernym of crystal ball; that is, orb is a word with a broader meaning than crystal ball:

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

Other hypernyms of crystal ball include ball, globe.

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

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