Orithil

The name of the third day of the week in Sindarin was dedicated to Ithil, the Moon. Its equivalent in Quenya was Isilya, with the same meaning. The idea of a day named for the Moon passed to Númenor, where the Elvish day-name was preserved, and on to Middle-earth, where it was rendered into the Common Tongue. There, it became Monendei, and later simply 'Monday'.