radiancy vs shininess

radiancy and shininess both are nouns.

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

As nouns, shininess is a hyponym of radiancy; that is, shininess is a word with a more specific, narrower meaning than radiancy:

radiancy: the quality of being bright and sending out rays of light
shininess: the visual property of something that shines with reflected light

Other hyponyms of radiancy include gleam, gleaming, glow, lambency, luster, lustre, sheen, burnish, gloss, glossiness, polish.

radiancy (noun)	shininess (noun)
the quality of being bright and sending out rays of light	the visual property of something that shines with reflected light