The name used by the Dúnedain for the tenth month of the year, also known by its Quenya name of Narquelië. The name came from the Sindarin words nar and peleth, and meant 'Sun-waning' (or more literally 'fire-fading'). It had originally been used by the Elves for one of their seasons, the period of later autumn more commonly called Firith.
The name for this season was adapted into the calendars of Men to mark one of the twelve months of their year. This month was approximately equivalent to modern October or, more precisely, running between 22 September and 21 October on a modern calendar. The version of Narbeleth used by Men was rather shorter than the original Narbeleth of the Elves, covering only about the first half of the Elves' autumn season. It also corresponded to the month of Halimath in the Shire Calendar.
In the earliest calendars of Men, Narbeleth followed directly from the preceding month of Yavannië, but in the modified Stewards' Reckoning, this arrangement was changed, and the feast-day of Yáviérë was introduced between the two months. In the New Reckoning introduced at the beginning of the Fourth Age, this single feast-day was expanded even further. The end of Yavannië was now marked by a day named Cormarë ('Ringday' in memory of the destruction of the Ring), followed by three Enderi or Middle-days, before the beginning of Narbeleth on this new dating system.
For more on the Elves' usage of this name for one of the six seasons of their year, see the separate entry for the season of Narbeleth.