The Collaborative International Dictionary of English v.0.48:

Agendum \A*gen"dum\ ([.a]*j[e^]n"d[u^]m), n.; pl. Agenda
   ([.a]*j[e^]n"d[.a]). [L., neut. of the gerundive of agere to
   act.]
   1. Something to be done; in the pl., a memorandum book; also,
      a list of items to be considered. See agenda.
      [1913 Webster]

   2. A church service; a ritual or liturgy. [In this sense,
      usually Agenda.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

agendum
    n 1: a list of matters to be taken up (as at a meeting) [syn:
         agenda, agendum, order of business]