The Collaborative International Dictionary of English v.0.48:

Passive \Pas"sive\, a. [L. passivus: cf. F. passif. See
   Passion.]
   1. Not active, but acted upon; suffering or receiving
      impressions or influences; as, they were passive
      spectators, not actors in the scene.
      [1913 Webster]

            The passive air
            Upbore their nimble tread.            --Milton.
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            The mind is wholly passive in the reception of all
            its simple ideas.                     --Locke.
      [1913 Webster]

   2. Receiving or enduring without either active sympathy or
      active resistance; without emotion or excitement; patient;
      not opposing; unresisting; as, passive obedience; passive
      submission.
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            The best virtue, passive fortitude.   --Massinger.
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   3. (Chem.) Inactive; inert; unreactive; not showing strong
      affinity; as, red phosphorus is comparatively passive.
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   4. (Med.) Designating certain morbid conditions, as
      hemorrhage or dropsy, characterized by relaxation of the
      vessels and tissues, with deficient vitality and lack of
      reaction in the affected tissues.
      [1913 Webster]

   Passive congestion (Med.), congestion due to obstruction to
      the return of the blood from the affected part.

   Passive iron (Chem.), iron which has been subjected to the
      action of heat, of strong nitric acid, chlorine, etc. It
      is then not easily acted upon by acids.

   Passive movement (Med.), a movement of a part, in order to
      exercise it, made without the assistance of the muscles
      which ordinarily move the part.

   Passive obedience (as used by writers on government),
      obedience or submission of the subject or citizen as a
      duty in all cases to the existing government.

   Passive prayer, among mystic divines, a suspension of the
      activity of the soul or intellectual faculties, the soul
      remaining quiet, and yielding only to the impulses of
      grace.

   Passive verb, or Passive voice (Gram.), a verb, or form
      of a verb, which expresses the effect of the action of
      some agent; as, in Latin, doceor, I am taught; in English,
      she is loved; the picture is admired by all; he is
      assailed by slander.
      [1913 Webster]

   Syn: Inactive; inert; quiescent; unresisting; unopposing;
        suffering; enduring; submissive; patient.
        [1913 Webster] Passive balloon

WordNet (r) 3.0 (2006):

passive
    adj 1: lacking in energy or will; "Much benevolence of the
           passive order may be traced to a disinclination to
           inflict pain upon oneself"- George Meredith [syn:
           passive, inactive] [ant: active]
    2: peacefully resistant in response to injustice; "passive
       resistance" [syn: passive, peaceful]
    3: expressing that the subject of the sentence is the patient of
       the action denoted by the verb; "academics seem to favor
       passive sentences" [ant: active]
    n 1: the voice used to indicate that the grammatical subject of
         the verb is the recipient (not the source) of the action
         denoted by the verb; "`The ball was thrown by the boy' uses
         the passive voice"; "`The ball was thrown' is an
         abbreviated passive" [syn: passive voice, passive]
         [ant: active, active voice]

Moby Thesaurus II by Grady Ward, 1.0:

211 Moby Thesaurus words for "passive":
   Laodicean, Olympian, abeyant, abject, accepting, accommodating,
   acquiescent, active, active voice, adapting, adaptive, adjusting,
   agreeable, aloof, amenable, apathetic, asleep, assenting, bearing,
   benumbed, blah, blank, blankminded, blase, bovine, calm,
   cataleptic, catatonic, centrist, comatose, complaisant, compliable,
   compliant, complying, consenting, contemplative, cool, dead,
   deferential, desensitized, detached, disinterested, dispassionate,
   do-nothing, docile, dopey, dormant, dull, empty, empty-headed,
   enduring, even, fatuous, fifty-fifty, flat, flexible, forbearing,
   foul, gentle, groggy, half-and-half, heartless, heavy,
   hebetudinous, hopeless, humble, idle, immobile, impartial,
   impassive, imperturbable, implicit, in a stupor, in abeyance,
   in suspense, inactive, inane, incogitant, independent, indifferent,
   inert, insouciant, laissez-aller, laissez-faire, lamblike, languid,
   languorous, latent, leaden, lethargic, lifeless, listless, logy,
   long-suffering, malleable, medio-passive, meditative, meek, middle,
   middle voice, midway, moderate, motionless, neuter, neutral,
   nirvanic, nonaligned, nonchalant, noncommitted, nondissenting,
   nonpartisan, nonresistant, nonresisting, nonresistive, nonviolent,
   numb, numbed, obedient, oblivious, on the fence, out of it, ovine,
   paralytic, paralyzed, passive voice, patient, phlegmatic, placid,
   pliable, pluckless, procrastinating, quiescent, quiet, quietist,
   quietistic, receptive, reconciled, reflexive, relaxed, repressed,
   resigned, sedentary, serene, servile, sheepish, slack, sleeping,
   sleepy, sluggish, slumbering, smoldering, soporific, spiritless,
   spunkless, stagnant, stagnating, standing, standpat, static,
   stationary, still, stoic, stolid, stupefied, subdued, submissive,
   subservient, supine, suspended, tacit, tame, third-force,
   third-world, thoughtfree, thoughtless, tolerant, torpid, tractable,
   tranquil, unaffected, unaroused, unassertive, uncaring,
   uncommitted, uncomplaining, unconcerned, undisclosed, unexpressed,
   unideaed, unintellectual, uninterested, uninvolved, unmoved,
   unmoving, unoccupied, unperturbed, unreasoning, unresistant,
   unresisting, unresponsive, unrevealed, unshaken, unthinking,
   untouched, vacant, vacuous, vegetable, vegetative, voice,
   withdrawn, yielding



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PASSIVE, com. law. All the sums of which one is a debtor. It is used in
contradistinction to active. (q.v.) By active debts are understood those
which may be employed in furnishing assets to a merchant to pay those which
he owes, which are called passive debts.