opacity vs softness

opacity and softness both are nouns.

Word	Noun	Adjective	Verb	Adverb
opacity	Yes	No	No	No
softness	Yes	No	No	No

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

opacity: the quality of being opaque to a degree; the degree to which something reduces the passage of light
softness: the quality of being indistinct and without sharp outlines

Other hyponyms of opacity include cloudiness, muddiness, murkiness, blurriness, fogginess, fuzziness, indistinctness.

opacity (noun)	softness (noun)
the quality of being opaque to a degree; the degree to which something reduces the passage of light	the property of giving little resistance to pressure and being easily cut or molded
incomprehensibility resulting from obscurity of meaning	a sound property that is free from loudness or stridency
the phenomenon of not permitting the passage of electromagnetic radiation	a disposition to be lenient in judging others
	acting in a manner that is gentle and mild and even-tempered
	the trait of being effeminate (derogatory of a man)
	the quality of being indistinct and without sharp outlines
	a visual property that is subdued and free from brilliance or glare
	a state of declining economic condition
	poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)
	the quality of weather that is deliciously mild and soothing