cryptograph vs written material

cryptograph and written material both are nouns.

Word	Noun	Adjective	Verb	Adverb
cryptograph	Yes	No	No	No
written material	Yes	No	No	No

As nouns, written material is a hypernym of cryptograph; that is, written material is a word with a broader meaning than cryptograph:

cryptograph: a piece of writing in code or cipher
written material: the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)

Other hypernyms of cryptograph include piece of writing, writing.

cryptograph (noun)	written material (noun)
a device for deciphering codes and ciphers	the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)
a piece of writing in code or cipher
a secret method of writing