Enderi were the three 'middle-days' unique to the Elven and the Númenórean calendars. As the enderi were counted outside the months, each month maintained equal length of days.
In the Reckoning of Rivendell the enderi were set between the astar of Yávië and Quellë. Every twelfth year, these Enderi were doubled.
In the Kings' Reckoning and Stewards' Reckoning, there was only one ender; the day of the middle of the year between Nárië and Cermië was called loëndë. In leap years (divisible by 4 but not 100) it was doubled to two enderi; in years divisible by 1000 loëndë was replaced by three enderi.
In the New Reckoning each year contained three enderi, between Yavannie and Narquelie; the middle of the three was referred to as loëndë.
 See also
- ↑ J.R.R. Tolkien, The Lord of the Rings, Appendix D, "The Calendars"