intercalate
To insert an extra leap day into a calendar in order to maintain synchrony with natural phenomena.
'[T]is wonderful where or when we ever got anything of this which we call wisdom, poetry, virtue. We never got it on any dated calendar day. Some heavenly days must have been intercalated somewhere.
To insert an extra month into a calendar for the same purpose, such as for the Hebrew calendar.
The Sages once overheard three shepherds discussing what weather is characteristic of Adar, and if that weather does not occur, it is not really Adar. As a result, the Sages intercalated the year and added Adar II.
To insert a substance between two or more molecules, bases, cells, or tissues.
To insert anything somewhere (especially between other things), such as an affix into a word. (Compare interpolate.)
... the personal pronouns which form the terminations of the verb, or by an intercalated suffix, the nature and relation of its objects and its subject , and to distinguish whether the object be animate or inanimate, ...
Where it comes from
The verb is first attested in 1614, the noun in 1964; borrowed from Latin intercalātus, perfect passive participle of intercalō (“to proclaim that a day, an event, etc. has been intercalated; to insert”) (see -ate (verb-forming suffix) and -ate (noun-forming suffix)), from inter- (“between, among”) + calō (“to call; to proclaim”).
Related words
Adapted from the Wiktionary entry intercalate (CC BY-SA 4.0).