quorum: [15] Quorum began life as the genitive plural of the Latin pronoun quī ‘who’. This appeared in former times in the Latin text of commissions issued to persons who because of some special expertise were required to act as justices of the peace in a particular case (if two JPs were required, for instance, the wording would be quorum vos … duos esse volumnus ‘of whom we wish that you … be two’). In due course the word came to be used as a noun, denoting the ‘number of justices who must be present in order to try the case’, and in the 17th century this was generalized to ‘minimum number of members necessary for a valid meeting’. [quorum etymology, quorum origin, 英语词源]