Definition
JAC is a Latin-derived abbreviation for *Jacobus*, the Latinized form of the name James. In legal and historical usage, it appears in two principal contexts:
1. **Statutory citation.** JAC (or Jac.) identifies statutes enacted during the reigns of the English kings named James — primarily James I (1603–1625) and James II (1685–1688). A citation such as "St. 1 Jac. II" refers to a statute passed in the first regnal year of James II.
2. **Law report citation.** JAC is the key component of the abbreviation *Cro. Jac.*, denoting the second part of Sir George Croke's collected reports — cases decided during the reign of James I. Croke's reports are divided into three parts by reign: *Cro. Eliz.* (Elizabeth I), *Cro. Jac.* (James I), and *Cro. Car.* (Charles I).
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Common Language
**Modern common usage (Wiktionary):** JAC appears as an initialism for several modern organizations and publications, including the Judicial Appointments Commission (UK), Joint Analysis Center, Joint Astronomy Centre, and Journal of Ancient Civilizations.
**Historical common usage (Webster's 1913):** Not defined as a standalone entry; "Jac." would have been recognized primarily as a learned abbreviation in legal and scholarly contexts.
The gap matters for researchers: encountering "JAC" or "Jac." in a legal document, brief, or treatise almost certainly signals the Latin abbreviation for *Jacobus* rather than any modern organizational acronym. Context — particularly the presence of a regnal number before or a report name before it — will confirm which usage applies.
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Common Confusion
*Cro. Jac.* is sometimes confused with *Cro. Car.* or *Cro. Eliz.* because Croke's three-part reports were published posthumously (1657–1661) and are frequently cited without clear indication of which volume is meant. *Jac.* specifically and exclusively refers to the James I volume. Researchers should also note that statutes cited as "Jac. I" and "Jac. II" refer to two different monarchs separated by sixty years, not to successive volumes of a single compilation.
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Why It Matters in Research
Researchers working in the Law Mind corpus will encounter JAC/Jac. almost exclusively in two situations: English statutory history and early modern English case law.
**Statutory traps.** Regnal year citations require knowing the precise dates of each reign to convert the abbreviation into a calendar year. "1 Jac. I" runs from March 1603; "1 Jac. II" runs from February 1685. Errors in identifying which James is meant — or in calculating the regnal year — can send a researcher to entirely the wrong statute or year.
**Croke's reports.** *Cro. Jac.* covers the period 1603–1625 and is an important source for early common law doctrine. The reports were compiled by Croke during his lifetime but edited and published by his son-in-law after his death, which affects their authority and internal consistency. Citations to *Cro. Jac.* in secondary treatises sometimes vary in page or folio reference depending on the edition consulted.
**Burrill's entry anomaly.** The Burrill's Law Dictionary source text supplied under JAC appears to be a fragment from an unrelated entry — likely relating to *iter* (eyre) and justices in eyre — that has been misattributed or misbound in the source corpus. Researchers should treat the Burrill's JAC entry with caution; it does not contain substantive information about the JAC abbreviation itself.
**Jurisdictional reach.** Because JAC citations appear in English sources, their relevance in American legal research is primarily historical: early American courts and treatise writers frequently cited English statutes and Croke's reports as persuasive authority, particularly in common law states before comprehensive codification.
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Historical Dictionary Support
Black's Law Dictionary (both the 1st and 2nd editions) are in complete agreement: JAC abbreviates *Jacobus*, used in statutory and report citations. The 2nd edition text is substantively identical to the 1st, reflecting the straightforward, settled nature of this abbreviation.
Anderson's Dictionary of Law offers the minimal but accurate gloss — "Jacobus: James, king James" — without elaboration on its citation functions.
Burrill's Law Dictionary, as noted above, provides no usable content on this entry as presented in the source corpus.
None of the historical sources address the full practical complexity of distinguishing James I from James II in statutory citations, nor do they note the editorial history of Croke's reports — gaps that matter for anyone actually using these citations in research.
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Jurisdictional Note
JAC as an abbreviation is an artifact of English legal practice under the regnal year citation system, which was formally abolished in England by the Acts of Parliament Numbering and Citation Act 1850. American legal sources adopted and perpetuated these English citations in treatises and early judicial opinions but did not independently generate new JAC citations after independence.
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