cryptograph vs piece of writing

cryptograph and piece of writing both are nouns.

Word	Noun	Adjective	Verb	Adverb
cryptograph	Yes	No	No	No
piece of writing	Yes	No	No	No

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

cryptograph: a piece of writing in code or cipher
piece of writing: 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 writing, written material.

cryptograph (noun)	piece of writing (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