|Days in the Shire Calendar|
Mersday was the sixth day of the week in the Shire Calendar and is equivalent with the Gregorian Saturday. In The Lord of the Rings Mersday is translated as Thursday according to the system in which Shire ‘Sunday’ and ‘Monday’ appear unchanged and Friday is last day of the week in translation of ‘Highday’.
Originally there was a six-day week - as Elves liked to reckon in sixes and twelves - but it was the Númenóreans who desired a seven-day week so they inserted an extra day after Heaven's Day. As they were great mariners they dedicated it to the sea, naming it Eärenya in Quenya (or Oraearon in Sindarin).