optical density vs density

optical density and density both are nouns.

Word	Noun	Adjective	Verb	Adverb
optical density	Yes	No	No	No
density	Yes	No	No	No

As nouns, density is a hypernym of optical density; that is, density is a word with a broader meaning than optical density:

optical density: (physics) a measure of the extent to which a substance transmits light or other electromagnetic radiation
density: the amount per unit size

Other hypernyms of optical density include denseness.

optical density (noun)	density (noun)
(physics) a measure of the extent to which a substance transmits light or other electromagnetic radiation	the amount per unit size
	the spatial property of being crowded together