watch glass vs watch crystal

watch glass and watch crystal both are nouns.

Word	Noun	Adjective	Verb	Adverb
watch glass	Yes	No	No	No
watch crystal	Yes	No	No	No

As nouns, watch glass and watch crystal are synonyms defined as:

watch glass and watch crystal: a protective cover that protects the face of a watch

Other synonyms of watch glass include crystal.

watch glass (noun)	watch crystal (noun)
a protective cover that protects the face of a watch	a protective cover that protects the face of a watch
laboratory glassware; a shallow glass dish used as an evaporating surface or to cover a beaker