secret writing vs cryptogram

secret writing and cryptogram both are nouns.

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

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

Other synonyms of secret writing include cryptograph.

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