Source : Webster's Revised Unabridged Dictionary (1913)

Week \Week\, n. [OE. weke, wike, woke, wuke AS. weocu, wicu,
   wucu; akin to OS. wika, OFries. wike, D. week, G. woche, OHG.
   wohha, wehha, Icel. vika, Sw. vecka, Dan. uge, Goth. wik?,
   probably originally meaning, a succession or change, and akin
   to G. wechsel change, L. vicis turn, alternation, and E.
   weak. Cf. {Weak}.]
   A period of seven days, usually that reckoned from one
   Sabbath or Sunday to the next.

         I fast twice in the week.                --Luke xviii.
                                                  12.

   Note: Although it [the week] did not enter into the calendar
         of the Greeks, and was not introduced at Rome till
         after the reign of Theodesius, it has been employed
         from time immemorial in almost all Eastern countries.
         --Encyc. Brit.

   {Feast of Weeks}. See {Pentecost}, 1.

   {Prophetic week}, a week of years, or seven years. --Dan. ix.
      24.

   {Week day}. See under {Day}.

Pentecost \Pen"te*cost\, n. [L. pentecoste, Gr. ? (sc. ?) the
   fiftieth day, Pentecost, fr. ? fiftieth, fr. ? fifty, fr. ?
   five. See {Five}, and cf. {Pingster}.]
   1. A solemn festival of the Jews; -- so called because
      celebrated on the fiftieth day (seven weeks) after the
      second day of the Passover (which fell on the sixteenth of
      the Jewish month Nisan); -- hence called, also, the {Feast
      of Weeks}. At this festival an offering of the first
      fruits of the harvest was made. By the Jews it was
      generally regarded as commemorative of the gift of the law
      on the fiftieth day after the departure from Egypt.

   2. A festival of the Roman Catholic and other churches in
      commemoration of the descent of the Holy Spirit on the
      apostles; which occurred on the day of Pentecost; --
      called also {Whitsunday}. --Shak.

Source : WordNet®

Feast of Weeks
     n : (Judaism) Jewish holy day celebrated on the sixth of Sivan
         to celebrate Moses receiving the Ten Commandments [syn: {Shavous},
          {Shabuoth}, {Shavuoth}, {Shavuot}, {Pentecost}]