The Collaborative International Dictionary of English v.0.48:

Accessary \Ac*ces"sa*ry\ (277), n.; pl. Accessaries. [Cf.
   Accessory and LL. accessarius.] (Law)
   One who, not being present, contributes as an assistant or
   instigator to the commission of an offense.
   [1913 Webster]

   Accessary before the fact (Law), one who commands or
      counsels an offense, not being present at its commission.


   Accessary after the fact, one who, after an offense,
      assists or shelters the offender, not being present at the
      commission of the offense.
      [1913 Webster]

   Note: This word, as used in law, is spelt accessory by
         Blackstone and many others; but in this sense is spelt
         accessary by Bouvier, Burrill, Burns, Whishaw, Dane,
         and the Penny Cyclopedia; while in other senses it is
         spelt accessory. In recent text-books on criminal law
         the distinction is not preserved, the spelling being
         either accessary or accessory.
         [1913 Webster]