quindene
/ˈkwɪndiːn/Christian Church. Now historical
noun
The fourteenth day after a festival (this being the fifteenth day when counted inclusively, following ancient Roman practice); (hence) the period of fifteen days beginning with the day of a festival.
Origin
Late 15th century; earliest use found in Robert Fabyan (d. 1513), chronicler. From post-classical Latin quindena (also quintana) fifteenth day after a festival, counting inclusively, period of fifteen days from classical Latin quīndēnī fifteen each from quīndecim fifteen + -ēnī, suffix forming distributive adjectives.