In Federal Commissioner of Taxation v Kentucky Fried Chicken, Justice Hope of the New South Wales court wrote:
"The word accessory can be either an adjective or a noun. In the Oxford English Dictionary the adjective is defined relevantly to mean: 'Coming as an accession; contributing in an additional and hence subordinate degree; additional, extra, adventitious.' As a noun its meaning is given as: 'An accessory thing; something contributing in a subordinate degree to a general result or effect; an adjunct, accompaniment.'
"In the Macquarie Dictionary, as an adjective its meaning is given as: 'contributing to a general effect; subsidiary.' As a noun its meaning is given as: 'a subordinate part or object; something added or attached for convenience, attractiveness, etc, such as a spotlight, heater, driving mirror, etc, for a vehicle'....
"As it seems to me, even without a context which may confirm such a conclusion, the word accessory whether used as an adjective or a noun does not necessarily connote that the accessory must be joined to something else. An object that is joined to another may well be an accessory although it will not necessarily be so. However, it may still be an accessory even though it is not joined.
"Adopting as a basis the meaning given in the Macquarie Dictionary, an article will be an accessory if it is a subordinate part or object, added or attached for convenience or effectiveness or other such reason."
In R v Silke, these words were used by the South African court:
"(1) The less valuable of two things so joined together as to be inseparable. The more valuable, to which the accessory accedes, is called the principal. (2) An accessory is a secondary, additional or nonessential item of equipment."
In the context of criminal law, Justice Bownes of the United States Court of Appeals summarized the law as follows in US v Anqiulo, including a helpful distinction of the related legal term, conspiracy:
"Conspiracy and accessory are two distinct offenses. That someone may have satisfied all the elements of conspiracy does not necessarily mean that he has satisfied all the elements of accessory. To be found an accessory, one must counsel, hire, or procure a felony to be committed. This means something more than mere acquiescence but does not require physical participation, if there is association with the venture and any significant participation in it. To prove a conspiracy, one must only show the formation of an unlawful agreement or combination."
Justice Willes wrote, in Stacey v Whitehurst:
"The law draws a distinction between principals in the first degree, principals in the second degree, and accessories - the latter being persons who aid or abet the principal offender in the commission of the offence, before or after."
Or these words of the Australian court in R v Webbe & Brown:
"The meaning of accessory particularly accessory before the fact may be important.... There must be some active proceeding on his part. He must procure, incite or in some other way encourage the act done by the principal."
It is not unusual for jurisdictions to define an accessory especially given that the consequences of being held liable for the ultimate actions of another can be substantial. In a 1992 case, State v Utterback, the Supreme Court of Nebraska reiterated this comprehensive description contained in the 1989 Reissue of the Nebraska Revised Statutes at §28-204:
"An accessory to a felony is one who, with the intent to interfere with, hinder, delay, or prevent the discovery, apprehension, prosecution, conviction, or punishment of another for an offense, (1) harbors or conceals the other; (2) provides or aids in providing a weapon, transportation, disguise, or other means of effecting escape or avoiding discovery or apprehension; (3) conceals or destroys evidence of the crime or tampers with a witness, informant, document, or other source of information, regardless of its admissibility in evidence; (4) warns the other of impending discovery or apprehension other than in connection with an effort to bring another into compliance with the law; (5) volunteers false information to a peace officer; or (6) by force, intimidation, or deception obstructs anyone in the performance of any act which might aid in the discovery, detection, apprehension, prosecution, conviction, or punishment of such person."
As a further example, §7.02 of the Texas Penal Code circa 2012:
"A person is criminally responsible for an offense committed by the conduct of another if ... acting with intent to promote or assist the commission of the offense, he solicits, encourages, directs, aids, or attempts to aid the other person to commit the offense."
- Federal Commissioner of Taxation v Kentucky Fried Chicken Pry Ltd., 81 ALR 35 (1988)
- R v Silke,  4 SA 298
- R v Webbe & Brown,  SASR 108
- Stacey v Whitehurst, 18 CBNS 344 (1895)
- State v Utterback, 485 NW 2d 760 (1992)
- US v Anqiulo, 89 F. 2d 1169 (1990)