quindene

The story

1. Latin · derived fromquīndēnī“15 each”
2. Medieval Latin · derived fromquindena
3. English todayquindene

From Medieval Latin quindena, from Latin quīndēnī (“15 each”), from the distributive form of quīndecim (“15”). It is used for a period of 14 days owing to the Roman and medieval practice of counting inclusively.