The Collaborative International Dictionary of English v.0.48:

Inelastic \In`e*las"tic\, a.
   1. Not elastic.
      [1913 Webster]

   2. (Economics) reacting little to changing price; -- of
      demand; as, Potatoes have an inelastic demand.
      [PJC]

WordNet (r) 3.0 (2006):

inelastic
    adj 1: not elastic; "economists speak of an inelastic price
           structure" [ant: elastic]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "inelastic":
   adamant, adamantine, cast-iron, dour, firm, flinty, grim, hard,
   hard-core, immovable, immutable, implacable, impliable, inductile,
   inexorable, inextensible, inextensile, inextensional, inflexible,
   intractable, intractile, intransigent, iron, irreconcilable,
   irresilient, nonelastic, nonstretchable, relentless, rigid,
   rigorous, rock-ribbed, steely, stern, stiff, stubborn, unaffected,
   unalterable, unbending, unchangeable, uncompromising, unextendible,
   unextensible, unflexible, ungiving, unlimber, unmalleable, unmoved,
   unpliable, unpliant, unrelenting, untractable, unyielding