The Collaborative International Dictionary of English v.0.48:

Immovable \Im*mov"a*ble\, a.
   1. Incapable of being moved; firmly fixed; fast; -- used of
      material things; as, an immovable foundation.
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            Immovable, infixed, and frozen round. --Milton.
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   2. Steadfast; fixed; unalterable; unchangeable; -- used of
      the mind or will; as, an immovable purpose, or a man who
      remains immovable.
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   3. Not capable of being affected or moved in feeling or by
      sympathy; unimpressible; impassive. --Dryden.
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   4. (Law.) Not liable to be removed; permanent in place or
      tenure; fixed; as, an immovable estate. See Immovable,
      n. --Blackstone.
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   Immovable apparatus (Med.), an appliance, like the plaster
      of paris bandage, which keeps fractured parts firmly in
      place.

   Immovable feasts (Eccl.), feasts which occur on a certain
      day of the year and do not depend on the date of Easter;
      as, Christmas, the Epiphany, etc.
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The Collaborative International Dictionary of English v.0.48:

Immovable \Im*mov"a*ble\, n.
   1. That which can not be moved.
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   2. pl. (Civil Law) Lands and things adherent thereto by
      nature, as trees; by the hand of man, as buildings and
      their accessories; by their destination, as seeds, plants,
      manure, etc.; or by the objects to which they are applied,
      as servitudes. --Ayliffe. --Bouvier.
      [1913 Webster]

WordNet (r) 3.0 (2006):

immovable
    adj 1: not able or intended to be moved; "the immovable hills"
           [syn: immovable, immoveable, stabile, unmovable]
    n 1: property consisting of houses and land [syn: real
         property, real estate, realty, immovable]

Moby Thesaurus II by Grady Ward, 1.0:

143 Moby Thesaurus words for "immovable":
   adamant, adamantine, affectless, anchored, anesthetized, arctic,
   at a standstill, autistic, blunt, cast-iron, catatonic, chill,
   chilly, cold, cold as charity, cold-blooded, coldhearted, constant,
   cool, determined, dispassionate, dogged, dour, drugged, dull,
   emotionally dead, emotionless, fast, firm, fixed, flinty, frigid,
   frosted, frosty, frozen, grim, hard, hard-core, heartless, icy,
   immobile, immotile, immotive, immutable, impassible, impassive,
   implacable, impliable, inalterable, inductile, inelastic,
   inexcitable, inexorable, inextensible, inextensile, inextensional,
   inflexible, insusceptible, intractable, intractile, intransigent,
   invariable, iron, irreconcilable, irremovable, irresilient, loyal,
   motionless, nonelastic, nonemotional, nonstretchable, obdurate,
   objective, obtuse, out of touch, passionless, pat, relentless,
   resolute, rigid, rigorous, riveted, rock-ribbed, rooted,
   self-absorbed, set, settled, sot, soulless, spiritless, stable,
   standpat, stationary, staunch, steadfast, steady, steely, stern,
   stiff, stony, stubborn, stuck, true, unaffected, unaffectionate,
   unalterable, unbending, unchangeable, uncompromising,
   undeflectable, unemotional, unextendible, unextensible, unfeeling,
   unflappable, unflexible, unflinching, ungiving, unimpassioned,
   unimpressionable, unlimber, unloving, unmalleable, unmodifiable,
   unmovable, unmoved, unmoving, unpassionate, unpliable, unpliant,
   unrelenting, unresponding, unresponsive, unshakable, unshakeable,
   unshaken, unsusceptible, unswerving, unsympathetic, untouchable,
   untractable, unwavering, unyielding