intercalary

This term is primarily used in technical, astronomical, or literary contexts. In chronometry, it describes the specific mechanism of adding time to synchronize a human-made calendar with the actual rotation of the Earth or its orbit around the sun, such as leap years or leap seconds.

When applied to literature or narrative structure, it refers to an interruption in the main plot. An intercalary chapter functions as a detour, providing thematic depth or historical context without advancing the primary chronological sequence of the story. It is a formal term and is rarely used in casual conversation.