Definition
A Latin term from Roman and medieval civil law meaning the decision, award, or judgment rendered by an arbiter or arbitrator. In legal usage, *arbitrium* denotes the authoritative determination issued at the conclusion of an arbitral proceeding — the product of the arbiter's discretion and judgment applied to the dispute before him.
The term carried two closely related senses in historical legal writing:
1. The award itself — the formal resolution of a dispute by a person chosen by the parties (or appointed by authority) to decide it. Equivalent to what modern law calls an arbitral award.
2. The discretionary judgment or will of a decision-maker — the exercise of reasoned discretion by a qualified person acting as judge of a matter. In this sense it shaded toward the concept of *boni viri arbitrium* (the judgment of a good man), a standard invoking equity and fairness rather than strict legal rule.
Common Confusion
*Arbitrium* is sometimes loosely equated with *arbitramentum*, another Latin term appearing in historical pleading for an arbitration award. The terms overlap substantially, but *arbitramentum* tends to appear in procedural contexts (as a plea or defense), while *arbitrium* more often refers to the substantive decision itself or the quality of discretion behind it. Neither should be confused with *arbiter* (the decision-maker) or *arbitrium boni viri* (the equitable standard), though all four concepts are closely entangled in the historical sources.
Why It Matters in Research
Researchers encountering *arbitrium* in pre-modern legal sources must be alert to context. The word does double duty: it can mean the concrete award document, or it can mean the abstract standard of judgment — the discretion a fair-minded person would exercise. These two senses appear side by side in the same sources, sometimes in the same paragraph.
The maxims attached to the term are the real research handles. *Arbitrium est judicium* (an award is a judgment) is quoted consistently across Black's, Rapalje & Lawrence, and Burrill, tracing back to Jenk. Cent. 137 (Jenkins' *Centuries of Cases*, a reliable citation). *Arbitrium est judicium boni viri, secundum æquum et bonum* (an award is the judgment of a good man, according to justice and equity) — cited to 3 Bulst. 64 (Bulstrode's *Reports*) — is the more substantive maxim and signals that arbitral awards were understood to carry equitable, not merely legal, force.
For corpus researchers in Law Mind, *arbitrium* is primarily a gateway term. It rarely appears in isolation in Anglo-American materials; instead, it surfaces embedded in Latin maxims, civil law treatises, and early common law pleading contexts. When you find it, look for the surrounding procedural framework: Is the source discussing the validity of an award? A plea in bar? The standard of review? The civil law pedigree of the term means it appears more heavily in equity-side materials, ecclesiastical court records, and admiralty sources than in common law pleading at nisi prius.
Modern law has replaced *arbitrium* entirely with English terminology, so the term's research relevance is essentially bounded to pre-nineteenth-century sources and civil law scholarship. It does not appear in modern arbitration statutes or rules.
Historical Dictionary Support
The four source dictionaries are in strong agreement on the core definition and cite the same two maxims with the same sources (Jenkins, Bulstrode). This consistency across Black's (both editions), Rapalje & Lawrence, and Burrill is itself informative: the term's meaning was settled and uncontested in the Anglo-American tradition.
Burrill adds a textual note — partially garbled in transmission — referencing *Reg. Orig. 111* (Registrum Omnium Brevium, the register of writs), which connects *arbitrium* to formal pleading practice. This is the most practically useful addition in Burrill, suggesting the term appeared in writ-era procedural documents, not just treatises.
What the historical dictionaries do not do is distinguish the equitable from the legal sense of the term, or flag the Roman law background that gave *boni viri arbitrium* its particular resonance in civil law systems. For that background, researchers should consult civil law treatises outside the common law dictionary tradition. The dictionaries also do not explain why *arbitrium est judicium* mattered doctrinally — the maxim served to legitimate arbitral awards by assimilating them to judicial judgments, a point with real consequences for enforcement.
Jurisdictional Note
*Arbitrium* as a live legal term belongs to the civil law tradition. In Anglo-American jurisdictions it survived primarily as a term of art in Latin maxims and historical pleading; it was never naturalized as an operative English-language term. Civil law jurisdictions (Scotland, Quebec, Louisiana, and continental European systems) retained the underlying concept longer and in more developed form.