PETRA

Definition

In old English law, a unit of weight equal to twelve and one-half pounds. Derived from the Latin and Medieval English legal vocabulary, petra denoted a stone weight used in commercial and agricultural measurement. The term appears in historical legal and administrative records where goods — particularly wool and other commodities — were weighed and taxed or sold by the stone.

Common Language

Modern common usage (Wiktionary): A female given name from Ancient Greek. Historical common usage: Not listed as a common English word in Webster's 1913; the term functioned primarily as a Latin borrowing in technical and legal contexts. Editorial note: The legal meaning of petra has no connection to its use as a personal name. A researcher encountering petra in a medieval or early modern legal document should treat it as a unit of measurement, not a proper noun.

Why It Matters in Research

Petra is a term confined almost entirely to medieval and early modern English legal records — manorial accounts, wool trade documents, customs rolls, and administrative compilations such as Fleta. Researchers working in those sources should be alert to the following: Measurement inconsistency: The stone as a unit of weight was notoriously variable across commodities and localities in medieval England. Burrill's citation to Fleta specifies twelve and one-half pounds, but the stone weight for wool, meat, and other goods was not uniform across time or region. A legal document citing petra may not correspond precisely to any single modern equivalent without additional context about the commodity and period. Fleta as the primary source: Both Black's dictionaries cite Cowell; Burrill goes further and cites Fleta directly, a 13th-century English legal treatise. Researchers seeking authoritative primary-source grounding should consult Fleta rather than rely solely on the dictionary gloss, as Fleta supplies the specific commodity and measurement context that the dictionaries compress. Latin terminology in English records: Petra appears in Latin-language legal instruments alongside other measurement terms (such as libra for pound or summa for a load). Misreading it as a personal name or place name — both plausible in Latin texts — would produce errors in interpreting transactions, tax records, or pleadings. Practical irrelevance in modern law: Petra has no current legal significance in common law jurisdictions. It surfaces only in historical legal research and should not be imported into any modern legal analysis.

Historical Dictionary Support

The three shelf sources are consistent in their core content: petra means a stone weight. Black's (both editions) supplies the bare definition with a citation to Cowell's legal interpreter. Burrill adds substantive value by citing Fleta directly and specifying the weight as twelve and one-half pounds — a detail Black's omits. This is a case where Burrill is the more useful research tool: it grounds the term in a primary source and distinguishes between the general sense (stone) and the technical measurement sense (a weight of 12.5 pounds). None of the historical dictionaries address the variability of the stone weight across commodities, which is a known complication in medieval commercial law. Researchers relying solely on the dictionary definition will have an accurate but incomplete picture. The absence of any entry in more recent editions of Black's confirms that petra dropped out of active legal usage well before the modern period.

Jurisdictional Note

Petra as a legal term of art is specific to the English common law tradition and its medieval administrative records. It does not appear as a recognized unit of measurement in Scots law, civil law systems, or American legal practice. Research use is limited to English historical legal materials.

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