Webster's Revised Unabridged Dictionary · 1913

Intercalary

Intercalary (?; 277) , adjective

[Latin intercalaris, intercalarius: compare French intercalaire. See Intercalate.]

1.
(Chron.) 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
Collocations (1)
Intercalary day (Medicine) , one on which no paroxysm of an intermittent disease occurs. — Mayne