Source : Webster's Revised Unabridged Dictionary (1913)

Intercalation \In*ter`ca*la"tion\, n. [L. intercalatio: cf. F.
   intercalation.]
   1. (Chron.) The insertion of a day, or other portion of time,
      in a calendar.

   2. The insertion or introduction of anything among others, as
      the insertion of a phrase, line, or verse in a metrical
      composition; specif. (Geol.), the intrusion of a bed or
      layer between other layers.

            Intercalations of fresh-water species in some
            localities.                           --Mantell.

Source : WordNet®

intercalation
     n : an insertion into a calendar [syn: {embolism}]