The Collaborative International Dictionary of English v.0.48:

Silent \Si"lent\, a. [L. silens, -entis, p. pr. of silere to be
   silent; akin to Goth. ana-silan.]
   1. Free from sound or noise; absolutely still; perfectly
      quiet.
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            How silent is this town!              --Shak.
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   2. Not speaking; indisposed to talk; speechless; mute;
      taciturn; not loquacious; not talkative.
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            Ulysses, adds he, was the most eloquent and most
            silent of men.                        --Broome.
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            This new-created world, whereof in hell
            Fame is not silent.                   --Milton.
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   3. Keeping at rest; inactive; calm; undisturbed; as, the wind
      is silent. --Parnell. Sir W. Raleigh.
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   4. (Pron.) Not pronounced; having no sound; quiescent; as, e
      is silent in "fable."
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   5. Having no effect; not operating; inefficient. [R.]
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            Cause . . . silent, virtueless, and dead. --Sir W.
                                                  Raleigh.
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   Silent partner. See Dormant partner, under Dormant.
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   Syn: Mute; taciturn; dumb; speechless; quiet; still. See
        Mute, and Taciturn.
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The Collaborative International Dictionary of English v.0.48:

Partner \Part"ner\ (p[aum]rt"n[~e]r), n. [For parcener,
   influenced by part.]
   1. One who has a part in anything with an other; a partaker;
      an associate; a sharer. "Partner of his fortune." --Shak.
      Hence:
      (a) A husband or a wife.
      (b) Either one of a couple who dance together.
      (c) One who shares as a member of a partnership in the
          management, or in the gains and losses, of a business.
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                My other self, the partner of my life. --Milton.
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   2. (Law) An associate in any business or occupation; a member
      of a partnership. See Partnership.
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   3. pl. (Naut.) A framework of heavy timber surrounding an
      opening in a deck, to strengthen it for the support of a
      mast, pump, capstan, or the like.
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   Dormant partner, or Silent partner. See under Dormant,
      a.
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   Syn: Associate; colleague; coadjutor; confederate; partaker;
        participator; companion; comrade; mate.
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The Collaborative International Dictionary of English v.0.48:

Dormancy \Dor"man*cy\, n. [From Dormant.]
   The state of being dormant; quiescence; abeyance.
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         It is by lying dormant a long time, or being . . . very
         rarely exercised, that arbitrary power steals upon a
         people.                                  --Burke.
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   2. (Her.) In a sleeping posture; as, a lion dormant; --
      distinguished from couchant.
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   Dormant partner (Com.), a partner who takes no share in the
      active business of a company or partnership, but is
      entitled to a share of the profits, and subject to a share
      in losses; -- called also sleeping partner or silent
      partner.

   Dormant window (Arch.), a dormer window. See Dormer.

   Table dormant, a stationary table. [Obs.] --Chaucer.
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WordNet (r) 3.0 (2006):

silent partner
    n 1: a partner (who usually provides capital) whose association
         with the enterprise is not public knowledge [syn: silent
         partner, sleeping partner]