Intercalary

Part of speech: adjective (a.)

1. Inserted or introduced among others in the calendar; as, an intercalary month, day, etc.; -- now applied particularly to the odd day (Feb. 29) inserted in the calendar of leap year. See Bissextile, n.

2. Introduced or inserted among others; additional; supernumerary. "Intercalary spines." Owen. This intercalary line . . . is made the last of a triplet. Beattie. Intercalary day (Med.), one on which no paroxysm of an intermittent disease occurs. Mayne.