出典:Wiktionary
From Latin agendum, substantive use of the neuter singular of agendus (“which ought to be done”), future passive participle (gerundive) of agō (“I do, act, make”).
agendum (複数形 agenda または agendums)
Agendum is a word now so common in the plural that its plural form agenda is now generally taken to be a collective singular form, with the special meaning of a list of tasks which are to be done. A similar case is datum and its plural data which is now commonly taken to be a collective singular and synonymous with 'information'.
agendum