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

The Collaborative International Dictionary of English v.0.48:

Voice \Voice\, n. [OE. vois, voys, OF. vois, voiz, F. voix, L.
   vox, vocis, akin to Gr. ? a word, ? a voice, Skr. vac to say,
   to speak, G. erw[aum]hnen to mention. Cf. Advocate,
   Advowson, Avouch, Convoke, Epic, Vocal, Vouch,
   Vowel.]
   1. Sound uttered by the mouth, especially that uttered by
      human beings in speech or song; sound thus uttered
      considered as possessing some special quality or
      character; as, the human voice; a pleasant voice; a low
      voice.
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            He with a manly voice saith his message. --Chaucer.
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            Her voice was ever soft,
            Gentle, and low; an excellent thing in woman.
                                                  --Shak.
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            Thy voice is music.                   --Shak.
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            Join thy voice unto the angel choir.  --Milton.
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   2. (Phon.) Sound of the kind or quality heard in speech or
      song in the consonants b, v, d, etc., and in the vowels;
      sonant, or intonated, utterance; tone; -- distinguished
      from mere breath sound as heard in f, s, sh, etc., and
      also whisper.
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   Note: Voice, in this sense, is produced by vibration of the
         so-called vocal cords in the larynx (see Illust. of
         Larynx) which act upon the air, not in the manner of
         the strings of a stringed instrument, but as a pair of
         membranous tongues, or reeds, which, being continually
         forced apart by the outgoing current of breath, and
         continually brought together again by their own
         elasticity and muscular tension, break the breath
         current into a series of puffs, or pulses, sufficiently
         rapid to cause the sensation of tone. The power, or
         loudness, of such a tone depends on the force of the
         separate pulses, and this is determined by the pressure
         of the expired air, together with the resistance on the
         part of the vocal cords which is continually overcome.
         Its pitch depends on the number of aerial pulses within
         a given time, that is, on the rapidity of their
         succession. See Guide to Pronunciation, [sect][sect] 5,
         146, 155.
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   3. The tone or sound emitted by anything.
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            After the fire a still small voice.   --1 Kings xix.
                                                  12.
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            Canst thou thunder with a voice like him? --Job xl.
                                                  9.
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            The floods have lifted up their voice. --Ps. xciii.
                                                  3.
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            O Marcus, I am warm'd; my heart
            Leaps at the trumpet's voice.         --Addison.
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   4. The faculty or power of utterance; as, to cultivate the
      voice.
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   5. Language; words; speech; expression; signification of
      feeling or opinion.
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            I desire to be present with you now, and to change
            my voice; for I stand in doubt of you. --Gal. iv.
                                                  20.
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            My voice is in my sword.              --Shak.
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            Let us call on God in the voice of his church. --Bp.
                                                  Fell.
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   6. Opinion or choice expressed; judgment; a vote.
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            Sic. How now, my masters! have you chose this man?
            1 Cit. He has our voices, sir.        --Shak.
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            Some laws ordain, and some attend the choice
            Of holy senates, and elect by voice.  --Dryden.
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   7. Command; precept; -- now chiefly used in scriptural
      language.
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            So shall ye perish; because ye would not be obedient
            unto the voice of the Lord your God.  --Deut. viii.
                                                  20.
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   8. One who speaks; a speaker. "A potent voice of Parliament."
      --Tennyson.
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   9. (Gram.) A particular mode of inflecting or conjugating
      verbs, or a particular form of a verb, by means of which
      is indicated the relation of the subject of the verb to
      the action which the verb expresses.
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   Active voice (Gram.), that form of the verb by which its
      subject is represented as the agent or doer of the action
      expressed by it.

   Chest voice (Phon.), a kind of voice of a medium or low
      pitch and of a sonorous quality ascribed to resonance in
      the chest, or thorax; voice of the thick register. It is
      produced by vibration of the vocal cords through their
      entire width and thickness, and with convex surfaces
      presented to each other.

   Head voice (Phon.), a kind of voice of high pitch and of a
      thin quality ascribed to resonance in the head; voice of
      the thin register; falsetto. In producing it, the
      vibration of the cords is limited to their thin edges in
      the upper part, which are then presented to each other.

   Middle voice (Gram.), that form of the verb by which its
      subject is represented as both the agent, or doer, and the
      object of the action, that is, as performing some act to
      or upon himself, or for his own advantage.

   Passive voice. (Gram.) See under Passive, a.

   Voice glide (Pron.), the brief and obscure neutral vowel
      sound that sometimes occurs between two consonants in an
      unaccented syllable (represented by the apostrophe), as in
      able (a"b'l). See Glide, n., 2.

   Voice stop. See Voiced stop, under Voiced, a.

   With one voice, unanimously. "All with one voice . . .
      cried out, Great is Diana of the Ephesians." --Acts xix.
      34.
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WordNet (r) 3.0 (2006):

passive voice
    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]