The Collaborative International Dictionary of English v.0.48:

Movable \Mov"a*ble\, a. [Cf. OF. movable. See Move.]
   1. Capable of being moved, lifted, carried, drawn, turned, or
      conveyed, or in any way made to change place or posture;
      susceptible of motion; not fixed or stationary; as, a
      movable steam engine. [Also spelled moveable.]

   Syn: transferable, transferrable, transportable.
        [1913 Webster]

   2. Changing from one time to another; as, movable feasts, i.
      e., church festivals, the date of which varies from year
      to year.
      [1913 Webster]

   Movable letter (Heb. Gram.), a letter that is pronounced,
      as opposed to one that is quiescent.

   Movable feast (Ecclesiastical), a holy day that changes
      date, depending on the lunar cycle. An example of such a
      day is Easter.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Feast \Feast\ (f[=e]st), n. [OE. feste festival, holiday, feast,
   OF. feste festival, F. f[^e]te, fr. L. festum, pl. festa, fr.
   festus joyful, festal; of uncertain origin. Cf. Fair, n.,
   Festal, F[^e]te.]
   1. A festival; a holiday; a solemn, or more commonly, a
      joyous, anniversary.
      [1913 Webster]

            The seventh day shall be a feast to the Lord. --Ex.
                                                  xiii. 6.
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            Now his parents went to Jerusalem every year at the
            feast of the passover.                --Luke ii. 41.
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   Note: An Ecclesiastical feast is called a immovable feast
         when it always occurs on the same day of the year;
         otherwise it is called a movable feast. Easter is a
         notable movable feast.
         [1913 Webster]

   2. A festive or joyous meal; a grand, ceremonious, or
      sumptuous entertainment, of which many guests partake; a
      banquet characterized by tempting variety and abundance of
      food.
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            Enough is as good as a feast.         --Old Proverb.
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            Belshazzar the King made a great feast to a thousand
            of his lords.                         --Dan. v. 1.
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   3. That which is partaken of, or shared in, with delight;
      something highly agreeable; entertainment.
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            The feast of reason, and the flow of soul. --Pope.
      [1913 Webster]

   Feast day, a holiday; a day set as a solemn commemorative
      festival.

   Syn: Entertainment; regale; banquet; treat; carousal;
        festivity; festival.

   Usage: Feast, Banquet, Festival, Carousal. A feast
          sets before us viands superior in quantity, variety,
          and abundance; a banquet is a luxurious feast; a
          festival is the joyful celebration by good cheer of
          some agreeable event. Carousal is unrestrained
          indulgence in frolic and drink.
          [1913 Webster]

WordNet (r) 3.0 (2006):

movable feast
    n 1: a religious holiday that falls on different dates in
         different years [syn: movable feast, moveable feast]