The Collaborative International Dictionary of English v.0.48:

Demand \De*mand"\, v. t. [imp. & p. p. Demanded; p. pr. & vb.
   n. Demanding.] [F. demander, LL. demandare to demand,
   summon, send word, fr. L. demandare to give in charge,
   intrust; de- + mandare to commit to one's charge, commission,
   order, command. Cf. Mandate, Commend.]
   1. To ask or call for with authority; to claim or seek from,
      as by authority or right; to claim, as something due; to
      call for urgently or peremptorily; as, to demand a debt;
      to demand obedience.
      [1913 Webster]

            This, in our foresaid holy father's name,
            Pope Innocent, I do demand of thee.   --Shak.
      [1913 Webster]

   2. To inquire authoritatively or earnestly; to ask, esp. in a
      peremptory manner; to question.
      [1913 Webster]

            I did demand what news from Shrewsbury. --Shak.
      [1913 Webster]

   3. To require as necessary or useful; to be in urgent need
      of; hence, to call for; as, the case demands care.
      [1913 Webster]

   4. (Law) To call into court; to summon. --Burrill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

demanding
    adj 1: requiring more than usually expected or thought due;
           especially great patience and effort and skill; "found
           the job very demanding"; "a baby can be so demanding"
           [ant: undemanding]

Moby Thesaurus II by Grady Ward, 1.0:

111 Moby Thesaurus words for "demanding":
   Herculean, Spartan, Spartanic, abstruse, accurate, arduous,
   astringent, attentive, austere, authoritarian, brutal, burdensome,
   cajoling, clamant, clamorous, close, coaxing, complex,
   conscientious, correct, critical, crying, delicate, detailed,
   difficile, difficult, dour, draining, dunning, exact, exacting,
   exigent, exorbitant, exquisite, extortionate, fine, finical,
   finicking, finicky, formidable, fussy, grasping, grievous, grim,
   hairy, hard, hard-earned, hard-fought, harsh, imperative,
   importunate, insistent, instant, intricate, jawbreaking, knotted,
   knotty, laborious, loud, mean, meticulous, minute, nagging, narrow,
   nice, no picnic, not easy, operose, oppressive, particular,
   persistent, pertinacious, pestering, plaguing, precise,
   precisianistic, precisionistic, pressing, punctilious, punctual,
   refined, religious, rigid, rigorous, rough, rugged, scrupulous,
   scrutinizing, set with thorns, severe, spiny, steep, stern,
   strenuous, strict, stringent, subtle, taxing, teasing, thorny,
   ticklish, toilsome, tough, tricky, trying, unsparing, uphill,
   urgent, weighty, wheedling, wicked