intercalate

Intercalate was formed from the Latin prefix inter-, meaning "between" or "among," and the Latin verb calāre, meaning "to proclaim" or "to announce." It was originally associated with proclaiming the addition of a day or month in a calendar. An instance of intercalation occurred in the earliest versions of the Roman calendar, which originally consisted of 304 days and 10 months and was determined by the lunar cycle (the remaining 61.25 days of winter were apparently ignored). According to some Roman legends, it was Numa Pompilius, the second king of Rome, who intercalated the months January and February. Eventually, the word's use broadened to include other instances of introducing new elements or layers into a preexisting system.