cryptogram vs written material

cryptogram and written material both are nouns.

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

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

cryptogram: 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 cryptogram include piece of writing, writing.

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