order of business vs agendum

order of business and agendum both are nouns.

Word	Noun	Adjective	Verb	Adverb
order of business	Yes	No	No	No
agendum	Yes	No	No	No

As nouns, order of business and agendum are synonyms defined as:

order of business and agendum: a list of matters to be taken up (as at a meeting)

Other synonyms of order of business include agenda.

order of business (noun)	agendum (noun)
a list of matters to be taken up (as at a meeting)	a list of matters to be taken up (as at a meeting)