sheen vs shininess

sheen and shininess both are nouns.

Word	Noun	Adjective	Verb	Adverb
sheen	Yes	No	No	No
shininess	Yes	No	No	No

As nouns, sheen and shininess are synonyms defined as:

sheen and shininess: the visual property of something that shines with reflected light

Other synonyms of sheen include luster, lustre.

sheen (noun)	shininess (noun)
the visual property of something that shines with reflected light	the visual property of something that shines with reflected light