steganography vs secret writing

steganography and secret writing both are nouns.

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

As nouns, steganography and secret writing are synonyms defined as:

Other synonyms of steganography include coding, cryptography.

steganography (noun)	secret writing (noun)
act of writing in code or cipher	act of writing in code or cipher
	a piece of writing in code or cipher