The Collaborative International Dictionary of English v.0.48:

Sleeping \Sleep"ing\,
   a. & n. from Sleep.
   [1913 Webster]

   Sleeping car, a railway car or carrriage, arranged with
      apartments and berths for sleeping.

   Sleeping partner (Com.), a dormant partner. See under
      Dormant.

   Sleeping table (Mining), a stationary inclined platform on
      which pulverized ore is washed; a kind of buddle.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sleep \Sleep\, v. i. [imp. & p. p. Slept; p. pr. & vb. n.
   Sleeping.] [OE. slepen, AS. sl?pan; akin to OFries. sl?pa,
   OS. sl[=a]pan, D. slapen, OHG. sl[=a]fan, G. schlafen, Goth.
   sl?pan, and G. schlaff slack, loose, and L. labi to glide,
   slide, labare to totter. Cf. Lapse.]
   1. To take rest by a suspension of the voluntary exercise of
      the powers of the body and mind, and an apathy of the
      organs of sense; to slumber. --Chaucer.
      [1913 Webster]

            Watching at the head of these that sleep. --Milton.
      [1913 Webster]

   2. Figuratively:
      (a) To be careless, inattentive, or uncouncerned; not to
          be vigilant; to live thoughtlessly.
          [1913 Webster]

                We sleep over our happiness.      --Atterbury.
          [1913 Webster]
      (b) To be dead; to lie in the grave.
          [1913 Webster]

                Them also which sleep in Jesus will God bring
                with him.                         --1 Thess. iv.
                                                  14.
          [1913 Webster]
      (c) To be, or appear to be, in repose; to be quiet; to be
          unemployed, unused, or unagitated; to rest; to lie
          dormant; as, a question sleeps for the present; the
          law sleeps.
          [1913 Webster]

                How sweet the moonlight sleep upon this bank!
                                                  --Shak.
          [1913 Webster]

WordNet (r) 3.0 (2006):

sleeping
    adj 1: lying with head on paws as if sleeping [syn:
           dormant(ip), sleeping]
    n 1: the state of being asleep [ant: waking]
    2: quiet and inactive restfulness [syn: quiescence,
       quiescency, dormancy, sleeping]
    3: the suspension of consciousness and decrease in metabolic
       rate

Moby Thesaurus II by Grady Ward, 1.0:

124 Moby Thesaurus words for "sleeping":
   abeyant, apathetic, asleep, asleep in Jesus, at rest,
   bereft of life, between the lines, breathless, called home,
   carrion, cataleptic, catatonic, comatose, covert, croaked, cryptic,
   dead, dead and gone, dead asleep, death-struck, deceased,
   deep asleep, defunct, delitescent, demised, departed,
   departed this life, destitute of life, done for, dopey, dormant,
   dull, esoteric, exanimate, fallen, fast asleep, finished,
   flaked-out, flat, food for worms, foul, gone, gone to glory,
   gone west, goofing off, groggy, heavy, hibernating, hidden,
   in abeyance, in suspense, inactive, inanimate, incautious, inert,
   languid, languorous, late, late lamented, latent,
   launched into eternity, leaden, lifeless, logy, lurking, martyred,
   muffled, mystic, napping, no more, nodding, obfuscated, oblivious,
   obscured, occult, off-guard, out, passed on, passive, phlegmatic,
   possible, potential, pushing up daisies, released, reposing,
   resting easy, sainted, sedentary, slack, sluggish, slumbering,
   smitten with death, smoldering, sound asleep, stagnant, standing,
   static, still, stillborn, submerged, suspended, taken away,
   taken off, tame, torpid, unalert, unaroused, uncautious,
   unconscious, under the surface, underlying, unguarded,
   unmanifested, unprepared, unready, unvigilant, unwary, unwatchful,
   veiled, virtual, with the Lord, with the saints, without life,
   without vital functions