Definition
ARM, as a legal term of art, operates primarily as a verb and as a root for compound constructions rather than as a standalone noun. Its legal significance falls into three distinct uses:
1. To arm (verb): To furnish or equip a person with a weapon or weapons. Relevant in criminal law contexts involving the enhancement of offenses where a defendant or co-defendant is armed during the commission of a crime.
2. Arms (noun, plural): Weapons, particularly those capable of offensive or defensive use in combat. The term appears most prominently in Second Amendment jurisprudence and in statutes governing the possession, carry, and use of weapons. "Arms" in constitutional usage encompasses instruments of offensive or defensive combat and has been interpreted by the Supreme Court to include firearms in common use for lawful purposes.
3. Armed (adjective): The status of possessing or carrying a weapon, typically a firearm or other deadly weapon, at the time of a criminal act. "Armed" status typically triggers sentencing enhancements, elevates offense grades, or defines distinct criminal offenses such as armed robbery or armed assault.
The singular noun "arm" (meaning a single weapon or limb) rarely appears as a freestanding legal term; its legal weight is carried almost entirely by the plural "arms" and the adjectival and verbal forms.
Common Language
Modern common usage (Wiktionary): To take by the arm; to take up in one's arms.
Historical common usage (Webster's 1913): The limb of the human body extending from the shoulder to the hand; anything resembling such a limb, including branches, projections, and appendages of instruments or machines.
The gap between common and legal meaning is significant. In ordinary English, "arm" refers primarily to the anatomical limb or, by extension, any limb-like projection. In law, "arm" and especially "arms" refers to weapons — a meaning that descends from a distinct historical usage unrelated to anatomy. A researcher encountering "arm" in a legal source should determine from context whether the anatomical or weapons-related sense is intended; in almost all legal and constitutional sources, the weapons meaning governs.
Common Confusion
"Arms" in constitutional law is sometimes conflated with "firearms" specifically. The constitutional term is broader: historically it encompassed edged weapons, pole arms, and other instruments of combat. Courts have had to determine which modern weapons fall within constitutional protection, and that analysis turns on whether the weapon is in common use and not primarily suited for illegal purposes. "Arms" is not synonymous with "guns" in either historical or current constitutional doctrine, though firearms are the paradigm case in modern litigation.
Recognized Forms
/SUBTYPES
Right to bear arms: The constitutional guarantee under the Second Amendment that individuals have a right to keep and carry arms, confirmed as an individual right in District of Columbia v. Heller (2008).
Armed offense: A statutory category elevating a base criminal offense — typically robbery, assault, or burglary — when the offender carries or uses a weapon during the commission of the crime.
Armed forces: A distinct compound term referring to a nation's military services. Shares the "arms" root but operates in an entirely different legal and administrative context; do not conflate with Second Amendment usage.
Why It Matters in Research
The central research challenge with "arm" and "arms" is tracking a term whose constitutional significance has been dramatically reshaped by modern case law. For most of American legal history, Second Amendment doctrine was understood in collective or militia terms; Heller (2008) and McDonald v. City of Chicago (2010) reoriented the analysis around individual rights. Historical sources — including nineteenth-century dictionaries and treatises — will reflect pre-Heller assumptions. A researcher using older materials to understand "arms" in constitutional context must account for this doctrinal shift.
In criminal law, "armed" is almost always a statutory term whose definition varies considerably by jurisdiction. Whether a particular object qualifies as a weapon, whether constructive possession satisfies the "armed" requirement, and what mental state (if any) applies to the armed element are all jurisdiction-specific questions. Corpus sources from different states may use identical language with materially different legal content underneath.
Historical legal sources frequently use "arms" in the militia and military context without intending to address individual rights at all. Burrill and similar nineteenth-century dictionaries provide limited guidance on the constitutional dimension because the individual-rights framework simply was not the dominant interpretive lens at the time of their compilation.
Researchers moving from "arm" or "arms" in constitutional materials will need to connect to proportionality doctrine, the "common use" test, and the historical-tradition methodology that courts have applied since Heller and Bruen (2022). The encyclopedia entries on Second Amendment doctrine are essential next stops.
Historical Dictionary Support
Burrill's Law Dictionary does not provide a substantive standalone entry for "arm" or "arms" as a primary legal term. The passage preserved in the source material addresses rules of legal argument (the a maiori ad minus maxim), not the term "arm" itself — suggesting the dictionary reference was captured from surrounding context rather than a direct entry. This is an important gap: nineteenth-century legal dictionaries, including Burrill, generally did not develop "arms" as a richly defined constitutional term because the individual-rights dimension of the Second Amendment was not then the focus of legal analysis. Researchers should treat the absence of robust historical dictionary treatment as itself informative — it reflects the doctrinal landscape of the period, not an oversight.
Jurisdictional Note
Second Amendment doctrine now sets a constitutional floor, but states vary substantially in how they regulate arms under state constitutional provisions, many of which were adopted independently and have their own interpretive traditions. In criminal law, the definition of "armed," the weapons included, and the sentencing consequences differ materially across jurisdictions.
Encyclopedia Cross-Reference
The Law Mind Constitutional Law Encyclopedia: The Second Amendment — Individual Right to Bear Arms (Heller)
The Law Mind Constitutional Law Encyclopedia: The Right to Bear Arms and State Militia (Historical Context of the Second Amendment)
The Law Mind Criminal Law Encyclopedia: Armed Robbery and Carjacking