intercalation(n = noun.time) embolism - an insertion into a calendar;
is a kind of interval, time interval
is a part of calendar

1.  The insertion of a day, or other portion of time, in a calendar. [1913 Webster]

2.  The insertion or introduction of anything among others, as the insertion of a phrase, line, or verse in a metrical composition; [1913 Webster]
"Intercalations of fresh-water species in some localities." [1913 Webster]

N  interposition, interjacence, intercurrence, intervenience, interlocation, interdigitation, interjection, interpolation, interlineation, interspersion, intercalation, interpenetration, permeation, infiltration, intervention, interference, intrusion, obtrusion, insinuation, insertion, dovetailing, embolism, intermediary, intermedium, go between, bodkin, intruder, interloper, parenthesis, episode, flyleaf, partition, septum, diaphragm, midriff, dissepiment, party wall, panel, room divider, halfway house, interjacent, intercurrent, intervenient, intervening, intermediate, intermediary, intercalary, interstitial, embolismal, parenthetical, episodic, mediterranean, intrusive, embosomed, merged, between, betwixt, twixt, among, amongst, amid, amidst, mid, midst, in the thick of, betwixt and between, sandwich-wise, parenthetically, obiter dictum.