The Collaborative International Dictionary of English v.0.48:

Special \Spe"cial\, a. [L. specialis, fr. species a particular
   sort, kind, or quality: cf. F. sp['e]cial. See Species, and
   cf. Especial.]
   1. Of or pertaining to a species; constituting a species or
      sort.
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            A special is called by the schools a "species". --I.
                                                  Watts.
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   2. Particular; peculiar; different from others;
      extraordinary; uncommon.
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            Our Savior is represented everywhere in Scripture as
            the special patron of the poor and the afficted.
                                                  --Atterbury.
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            To this special evil an improvement of style would
            apply a special redress.              --De Quincey.
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   3. Appropriate; designed for a particular purpose, occasion,
      or person; as, a special act of Parliament or of Congress;
      a special sermon.
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   4. Limited in range; confined to a definite field of action,
      investigation, or discussion; as, a special dictionary of
      commercial terms; a special branch of study.
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   5. Chief in excellence. [Obs.]
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            The king hath drawn
            The special head of all the land together. --Shak.
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   Special administration (Law), an administration limited to
      certain specified effects or acts, or one granted during a
      particular time or the existence of a special cause, as
      during a controversy respecting the probate of a will, or
      the right of administration, etc.

   Special agency, an agency confined to some particular
      matter.

   Special bail, Bail above, or Bail to the action (Law),
      sureties who undertake that, if the defendant is
      convicted, he shall satisfy the plaintiff, or surrender
      himself into custody. --Tomlins. --Wharton (Law Dict.).

   Special constable. See under Constable. --Bouvier.

   Special damage (Law), a damage resulting from the act
      complained of, as a natural, but not the necessary,
      consequence of it.

   Special demurrer (Law), a demurrer for some defect of form
      in the opposite party pleading, in which the cause of
      demurrer is particularly stated.

   Special deposit, a deposit made of a specific thing to be
      kept distinct from others.

   Special homology. (Biol.) See under Homology.

   Special injuction (Law), an injuction granted on special
      grounds, arising of the circumstances of the case.
      --Daniell.

   Special issue (Law), an issue produced upon a special plea.
      --Stephen.

   Special jury (Law), a jury consisting of persons of some
      particular calling, station, or qualification, which is
      called upon motion of either party when the cause is
      supposed to require it; a struck jury.

   Special orders (Mil.), orders which do not concern, and are
      not published to, the whole command, such as those
      relating to the movement of a particular corps, a detail,
      a temporary camp, etc.

   Special partner, a limited partner; a partner with a
      limited or restricted responsibility; -- unknown at common
      law.

   Special partnership, a limited or particular partnership;
      -- a term sometimes applied to a partnership in a
      particular business, operation, or adventure.

   Special plea in bar (Law), a plea setting forth particular
      and new matter, distinguished from the general issue.
      --Bouvier.

   Special pleader (Law), originally, a counsel who devoted
      himself to drawing special counts and pleas; in a wider
      sense, a lawyer who draws pleadings.

   Special pleading (Law), the allegation of special or new
      matter, as distingiushed from a direct denial of matter
      previously alleged on the side. --Bouvier. The popular
      denomination of the whole science of pleading. --Stephen.
      The phrase is sometimes popularly applied to the specious,
      but unsound, argumentation of one whose aim is victory,
      and not truth. --Burrill.

   Special property (Law), a qualified or limited ownership
      possession, as in wild animals, things found or bailed.

   Special session, an extraordinary session; a session at an
      unusual time or for an unusual purpose; as, a special
      session of Congress or of a legislature.

   Special statute, or Special law, an act of the
      legislature which has reference to a particular person,
      place, or interest; a private law; -- in distinction
      from a general law or public law.

   Special verdict (Law), a special finding of the facts of
      the case, leaving to the court the application of the law
      to them. --Wharton (Law Dict.).
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   Syn: Peculiar; appropriate; specific; dictinctive;
        particular; exceptional; singular. See Peculiar.
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Bouvier's Law Dictionary, Revised 6th Ed (1856):

SPECIAL PLEA IN BAR. One which advances new matter. It differs from the
general in this, that the latter denies some material allegation, but never
advances new matter. Gould on Pl. c. 2, Sec. 38.