the GNU version of the Collaborative International Dictionary of English
n. Something to be done; in the pl., a memorandum book; also, a list of items to be considered. See agenda.
n. A church service; a ritual or liturgy. [In this sense, usually Agenda.]
The Century Dictionary and Cyclopedia
n. A thing to be done: usually in the plural, things to be done; duties.
n. Especially— Matters of ecclesiastical practice; ritual or liturgy. As a collective singular, a memorandum-book.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a list of matters to be taken up (as at a meeting)
Word Usage
"Similarly, agenda has taken on a singular life of its own (distinct from the near-obsolete agendum) and has given rise to the standard plural agendas."