Eärenya

The original week of the Elves had only six days, but when it was adopted in Númenor, the Men of that Isle preferred a seven-day weekly cycle. So, they added a seventh day between Menelya and Valanya. Being great mariners and explorers, they chose to name this new sixth day of the week after the Sea that surrounded their island home: Eärenya. When the seven-day week of Númenor was adopted in Middle-earth, so was this new day, and thus even in regions far from the coast, the 'Sea-day' still remained a part of the week.