secrecy vs hiddenness

secrecy and hiddenness both are nouns.

Word	Noun	Adjective	Verb	Adverb
secrecy	Yes	No	No	No
hiddenness	Yes	No	No	No

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

Other hyponyms of secrecy include covertness, bosom, confidentiality, hiding.

secrecy (noun)	hiddenness (noun)
the trait of keeping things secret	the state of being covert and hidden
the condition of being concealed or hidden