The last of the six days that made up the Elves' week. Orbelain is a Sindarin name, and the day was also know by the name Rodyn in the same language. In Quenya, the same day was given the names Valanya or Tárion. All these names have approximately the same meaning, referring to a day dedicated to the Valar or Powers. The same tradition was ultimately transmitted to Middle-earth, where the last day of the week became known as 'Highday'.
Notes
1
The Elvish diphthong ai is pronounced like the English word 'eye', so the last syllable of Orbelain sounds like English 'line' rather than 'lane'. Belain was the Sindarin version of the more familiar Quenya word Valar, referring to the Powers of the Undying Lands beyond the Western Sea.