1650s, from Latin agenda, literally "things to be done," neuter plural of agendus, gerundive of agere "to do" (see act (n.)). Originally theological (opposed to matters of belief), sense of "items of business to be done at a meeting" first attested 1882. "If a singular is required (=one item of the agenda) it is now agendum, the former singular agend being obsolete" [Fowler].
