cryptogram vs piece of writing

cryptogram and piece of writing both are nouns.

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

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

cryptogram: 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 cryptogram include writing, written material.

cryptogram (noun)	piece of writing (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)