secret writing vs coding

secret writing and coding both are nouns.

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

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

Other synonyms of secret writing include cryptography, steganography.

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