cryptogram vs secret writing

cryptogram and secret writing both are nouns.

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

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

Other synonyms of cryptogram include cryptograph.

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