Week

Elves
Most cultures of Middle-Earth used a system of a seven-day week, the Elves however, being immortal used a basic unit of counting time known as the yén or "great Year", corresponding roughly to 144 löar or coranari, sun-rounds or Sun-years. So very short periods of time such as weeks were far less important to them.

The Eldar, in the days of wandering prior to the rise of sun and moon, had adapted the "enquië", a six-day week. In Valinor the Elves adapted the "lemnar" or Valian Week of 5 days.A lesser known system of counting time was the "kainendan" or valian forthnight, a system of unit of time equal to 2 weeks or 14 days in which every day had it's own distinctive name.

After the destruction of the Trees and the rising of Sun and Moon however even elvish calculation of times or reckoning was subject of changes and the "otsola", an originally less known seven-day week now became more important.The Sindar in Beleriand continued the eldarin five-day week, which they called "lefnar" or "lefnor" with an additional secondary "ochlad", sun- or seven-day week.

Early Eldarin:
The enquië or quendian six-day week:
 * 1 - Elenya (Q."Star-Day") or Argilion
 * 2 - Anarya (Q."Sun-Day") or Aranor
 * 3 - Isilya (Q."Moon-Day") or Arithil
 * 4 - Aldúya (Q."Tree-Day") or Argalad 
 * 5 - Menelya (Q."Heaven's Day) or Arvenel
 * 6 - Valanya, Valarya (Q."Day of the Powers") or Tárion ("Great- or High Day")

Valinorian:
The lemnar or valian five-day week:
 * 1 - Are Manwen (Q. "Day of Manwe")
 * 2 - Ar Ulmon (Q."Day of Ulmo")
 * 3 - Are Veruen (Q."Day of the Spouses")
 * 4 - Are Fanturion (Q. Day of the Spirit-Lords")
 * 5 - Neldion (Q."Day of the Three")

Seven Days of the Otsola:
 * 1 - Múrien or Olórien (Q. "Dream-" or "Slumber-Day")
 * 2 - Fuinen (Q. "Fog-" or "Dark Day")
 * 3 - Taimoinen (Q. "Sky-Day")
 * 4 - Falassien (Q. "Coast-Day")
 * 5 - Palúrien(Q. "Wide Earth Day" or "Yavanna's Day")
 * 6 - Sainen (Q. "Fire-day")
 * 7 - Poldórien (Q. "Strength-" or "Might-Day")

kainendan or Valian fortnight:
 * Ulmosan or Vaisan
 * Aulisan or Marasan
 * Fantóran
 * Poldosan or Tulkassan
 * Falmasan
 * Makarnisan
 * Manwisan or Súlisan


 * Vardasan or Tinwesan
 * Qalmisan
 * Vanasan or Koirisan
 * Nessaran
 * Onensan
 * Salmaran or Omaran
 * Kémisan

Beleriandic
The lefnor or sindarian six-day week: 1 -Orgilion (S."Star-Day") 2 -Oranor (S."Sun-Day") 3 -Orithil (S."Moon-Day") 4 -Orlaladhad or Orgaladh (S."Tree-Day") 5 -Ormenel (S."Heaven's Day) 6 -Orbelain (S."Day of the Powers") or Rodyn (S."Powers")

Men
The Edain originally had adapted the Calendar of the Sindar, their númenórean descendants however later modified the elven calendar of Beleriand to their needs, eventually also drawing from earlier pre-beleriandic customs among men.With the rising of the Sun the mortals had started to calculate time with the rounds of the sun and invented a primitive solar-calendar with a year of approximately 365 days divided into twelve "Sâti" or months of each 30 days, each Sât divided into four "Otglâtai", weeks of seven days each. This early edainic Week was however not very efficient and so the Númenóreans modified it on base of the earlier elvish reckoning and the Noldorian "otsolë" or seven-day week by adding Eärenya, a seventh Day, between the original fifth and sixth day of the Eldarin Week.The Númenóreans originally used the Quenya Names of the Weekdays, later in the third Age however in the Realms of the Elendili the Sindarin Names became more common. The simple folk, lesser men and even non-mannish folk such as the Hobbits of the Shire often adapted simple translations into Westron.

The Númenorean Week:
1 - Elenya 2 - Anarya 3 - Isilya  4 - Aldëa 5 - Menelya 6 - Eärenya  7 - Valanya

The Week in the later Kingdoms of Gondor, Arthedain, Cardolan and Rhudaur
1 -Orgilion 2 -Oranor 3 -Orithil 4 -Orgaladh 5 -Ormenel 6 -Oraeron 7 -Orbelain

The Westron Names of Days in the Hobbit-Week
1 -Sterday, archaic: Sterrendei 2 -Sunday, archaic: Sunnendei 3 -Monday, archaic: Monendei 4 -Trewsday, archaic: Trewesdei 5 -Hevensday (Hensday), archaic: Hevenesdei 6 -Mersday, archaic: Meresdei 7 -Highday, archaic: Hihdei