A repertoire is a collection of things someone or someones have ready to perform (usually music, plays, and dances). Repertory is used to denote a work in rotation or a performer or company that rotate what they perform rather than performing the same work multiple times in a row (repertory theatre, repertory actor, to perform in repertory). Both words developed from the same Latin root, repertorium (inventory), and their branching meanings have only been attested to the nineteenth century.