dithyramb vs piece of writing

dithyramb and piece of writing both are nouns.

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

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

dithyramb: a wildly enthusiastic speech or piece of writing
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 dithyramb include writing, written material, address, speech.

dithyramb (noun)	piece of writing (noun)
(ancient Greece) a passionate hymn (usually in honor of Dionysus)	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 wildly enthusiastic speech or piece of writing