poem vs abecedarius

poem and abecedarius both are nouns.

Word	Noun	Adjective	Verb	Adverb
poem	Yes	No	No	No
abecedarius	Yes	No	No	No

As nouns, abecedarius is a hyponym of poem; that is, abecedarius is a word with a more specific, narrower meaning than poem:

poem: a composition written in metrical feet forming rhythmical lines
abecedarius: a poem having lines beginning with letters of the alphabet in regular order

poem (noun)	abecedarius (noun)
a composition written in metrical feet forming rhythmical lines	a poem having lines beginning with letters of the alphabet in regular order