epact
noun
ˈē-ˌpakt 
ˈe-
ˈe- : a period added to harmonize the lunar with the solar calendar
Word History
Etymology
Middle French epacte, from Late Latin epacta, from Greek epaktē, from epagein to bring in, intercalate, from epi- + agein to drive — more at agent
First Known Use
1588, in the meaning defined above