from
The Collaborative International Dictionary of English v.0.48
Intercalary \In*ter"ca*la*ry\ (?; 277), a. [L. intercalaris,
intercalarius: cf. F. intercalaire. See {Intercalate}.]
[1913 Webster]
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.
[1913 Webster]
2. Introduced or inserted among others; additional;
supernumerary. "Intercalary spines." --Owen.
[1913 Webster]
This intercalary line . . . is made the last of a
triplet. --Beattie.
[1913 Webster]
{Intercalary day} (Med.), one on which no paroxysm of an
intermittent disease occurs. --Mayne.
[1913 Webster]