The word is a Latin plural meaning "things that must be done," repurposed into a singular noun.
The word agenda is the neuter plural of the Latin gerundive agendum, derived from the verb agere, meaning "to do" or "to drive."1 In Latin, agenda meant "things that must be done," a list of obligations rather than a schedule. The word entered English in the early seventeenth century in ecclesiastical contexts, referring to a ritual or liturgical order of service.
By the mid-seventeenth century, the word had moved from churches to meeting rooms. It began to describe any list of matters to be discussed or acted upon in a formal gathering.2 The grammatical shift was significant. English speakers treated the Latin plural as a singular noun, requiring a new plural, "agendas," a construction that would have struck a Latin speaker as redundant.
The figurative sense of agenda as a hidden plan or secret set of goals emerged in the twentieth century. The phrase "hidden agenda" became common in political and organizational language by the 1960s and 1970s.3 A word that originally described duties to be performed had acquired an undertone of suspicion, as though any list of priorities concealed a less visible set of motives.
In the modern meeting, whoever sets the agenda determines which topics receive attention and which are excluded. The person who controls the list controls the room.