Agendum is singular. Agenda or agendums is plural.
The word agendum has become almost extinct. Originally agenda was the plural of agendum, meaning 'a thing to be done'. However, it became applied to a list of things to be done, and in this, the most usual modern sense, agenda has become firmly singular (replacing agendum), with the plural agendas. Compare with data.
Are is plural. "Is" is singular. For example, "There is a glove on the chair". That is singular. "There are gloves on the chair". That is plural.
Who may be singular or plural.
diagnosis is singular diagnoses is plural sis = singular ses = plural
Atrium is singular - the plural is atria.
"Agendum" is the singular form of the word. The plural form is "agenda."
The singular form is agendum. The plural forms are agenda or agendums.
Agenda was previously the plural form of the original singular form "agendum".
The word agendum has become almost extinct. Originally agenda was the plural of agendum, meaning 'a thing to be done'. However, it became applied to a list of things to be done, and in this, the most usual modern sense, agenda has become firmly singular (replacing agendum), with the plural agendas. Compare with data.
Although agenda is the plural of agendum in Latin, in standard modern English it is a normal singular noun with a normal plural form (agendas).
its agendumia
Agenda. Although few people use the word agendum any more.
agenda.
Agenda
english plural - agenda
agenda
When changing a plural word with the ending "a" to a singular word, you would typically remove the "a" and the word may change to a different form altogether. For example, "agenda" changes to "agendum."