[Kagome...] If you have a lst of things to be done (from the latin gerundive), or an agenda, and it only contains one item, it is still a list of things to be done. So I disagree, and would say that an agenda for a meeting is always an agenda, regardless of how many items are on it. More specifically, each item on an agenda would be an agendum.

[Kag] And you got the singular of Nazi wrong too; it's Nazus. :-)

[Phil] I have it on very good authority that each thing on an agenda is an itum.

[Phil] I have a "Keep Calm and Carry On" t-shirt. frogstar has one that says "Now Panic and Freak Out". To date I don't think we've worn them at the same time.

[KS] A datum is a data point and so is a count noun with a plural of data. However data meaning information is a mass noun and takes a singular agreement.