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.
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.
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.