1. A guardian or keeper; a person who has charge of something.
Usage: archaic or formal; primarily used in historical, legal, or ecclesiastical contexts
2. In medieval and early modern England, a royal official appointed to manage the lands or affairs of a minor or vacant estate.
Usage: historical; legal
3. In the Roman Catholic Church, a superior officer of a Franciscan province or convent.
Usage: ecclesiastical; religious

Examples

• The custos of the monastery oversaw all the monks and their daily duties.
• In medieval times, a custos was appointed to protect the interests of a young heir.
• The custos rotulorum held responsibility for the records and seal of the county.
• The Franciscan custos led the friars in their spiritual and communal life.
• As custos of the library, she ensured all manuscripts were properly preserved.