gesso vs gypsum

gesso and gypsum both are nouns.

Word	Noun	Adjective	Verb	Adverb
gesso	Yes	No	No	No
gypsum	Yes	No	No	No

As nouns, gypsum is a hypernym of gesso; that is, gypsum is a word with a broader meaning than gesso:

gesso: gypsum or plaster of Paris spread on a surface to make it suitable for painting or gilding (or a surface so prepared)
gypsum: a common white or colorless mineral (hydrated calcium sulphate) used to make cements and plasters (especially plaster of Paris)

Other hypernyms of gesso include plaster, plaster of Paris.

gesso (noun)	gypsum (noun)
gypsum or plaster of Paris spread on a surface to make it suitable for painting or gilding (or a surface so prepared)	a common white or colorless mineral (hydrated calcium sulphate) used to make cements and plasters (especially plaster of Paris)