intercalary

9.9

Added to a calendar to keep the year in line with the seasons, like a leap day

adjective
/ˌɪntərˈkeɪləri/

Specialized

: intercalado

The intercalary month was added to the calendar to align the lunar cycles with the solar year.

Examples

An intercalary day is included every four years to help keep our calendar synchronized with the Earth's orbit.
Tennyson also recited "The splendour falls on castle walls" and "Ask me no more," both short intercalary lyrics taken from his long narrative poem The Princess: A Medley.

Academic text (2017)
February has an intercalary day in leap years, which adds an extra day to the month.

Compounds

intercalary year

Specialized

8.3

A year with an extra day added to February to keep the dates matching the seasons

Surface Forms

intercalary positive

Morphology

intercalary = intercalate (semi-transparent) = inter + cal + ary

The adjective is a regular suffixation of -ary to the verb 'intercalate', but the verb and the root 'cal' are rare and calendar-specific, making the relation only partially obvious to typical learners.

Etymology

Intercalary comes from the Latin part inter- meaning 'between' and a root you can see in calendar, the word for a list of days and months. So an intercalary day or month is one 'inserted between' the usual ones, like February 29 added to the calendar to keep the year correct.