cover glass vs sheet glass

cover glass and sheet glass both are nouns.

Word	Noun	Adjective	Verb	Adverb
cover glass	Yes	No	No	No
sheet glass	Yes	No	No	No

As nouns, sheet glass is a hypernym of cover glass; that is, sheet glass is a word with a broader meaning than cover glass:

cover glass: a small and very thin piece of glass used to cover the specimen on a microscope slide
sheet glass: glass formed into large thin sheets

Other hypernyms of cover glass include plate glass.

cover glass (noun)	sheet glass (noun)
a small and very thin piece of glass used to cover the specimen on a microscope slide	glass formed into large thin sheets