intercalary

Intercalary is an adjective meaning inserted or introduced between other elements. The word comes from Medieval Latin intercalaris, from intercalare, “to insert between.” It is used in several fields to describe something put into an interval or between regular parts of a system.

In calendrical usage, an intercalary period is added to keep a calendar in alignment with the solar year or other cycles. The most familiar example is the leap day, February 29, added during leap years in the Gregorian calendar. Some calendars insert an intercalary month rather than an extra day; this occurs in lunisolar systems such as the Hebrew calendar (which adds Adar II during leap years) and in various traditional Hindu and other lunisolar calendars. The exact rules for intercalation vary by system, but the goal is to compensate for the difference between a year or month and the astronomical cycle.

In botany, intercalary refers to growth at the base of plant parts or along a stem, often driven by intercalary meristems. This type of growth lets certain plants, notably many grasses, extend leaves or recover quickly after grazing or mowing, while the main growing tip remains protected.

The term is occasionally used in other disciplines to denote material or elements inserted within a sequence or structure, but its core sense remains insertion between regular components.