encryption vs secret writing

encryption and secret writing both are nouns.

Word	Noun	Adjective	Verb	Adverb
encryption	Yes	No	No	No
secret writing	Yes	No	No	No

As nouns, secret writing is a hypernym of encryption; that is, secret writing is a word with a broader meaning than encryption:

Other hypernyms of encryption include coding, cryptography, steganography.

encryption (noun)	secret writing (noun)
the activity of converting data or information into code	act of writing in code or cipher
	a piece of writing in code or cipher