Definition
A Latin term from old English law denoting a "rase," a unit of measure applied specifically to onions. One rasus comprised twenty flones, with each flon containing twenty-five heads, yielding a total of five hundred heads of onions per rasus. The term appears in medieval commercial and agricultural law as a standardized measure for purposes of trade regulation, market oversight, and the assessment of duties or tolls on produce.
Why It Matters in Research
Rasus is encountered almost exclusively in contexts involving medieval English market law, assize provisions, and records of manorial or borough trade regulation. Researchers working in pre-modern English legal history — particularly those examining the Fleta or similar thirteenth-century compilations — may encounter the term when tracing the legal standardization of weights and measures, a function that English law took seriously as a matter of commercial fairness and royal prerogative. The term has no surviving practical significance in modern law and will not appear in post-medieval case law or statutes.
The principal trap for researchers is the partial entry in Black's Law Dictionary (2nd Ed.), which appends the word "Plunder" after the definition with no explanation, suggesting either a printing artifact, a misbound entry, or the beginning of a separate headword that was not cleanly separated. Treat this addition with caution; neither Burrill nor the first edition of Black's connects rasus to any meaning related to plunder. A researcher relying on the second edition alone could be misled into thinking the term carried a secondary meaning it does not appear to have had.
Because rasus defines a quantity of a specific agricultural commodity rather than a legal right or remedy, it belongs to the category of medieval legal metrology — the body of law governing standardized measures. Researchers tracing the history of weights-and-measures law in England should note that such measures were frequently the subject of royal ordinances and statutes, and that the legal vocabulary of medieval metrology is scattered across a range of sources including the Fleta, Britton, and various assizes. Cross-referencing those sources is often necessary to reconstruct the full regulatory context in which a term like rasus operated.
Historical Dictionary Support
All three source dictionaries are in complete agreement: rasus means a rase of onions measured at twenty flones of twenty-five heads each, and all three cite the same authority — Fleta, lib. 2, c. 12, § 12. This uniformity reflects that the term is narrow, archaic, and traceable to a single primary source. No dictionary offers elaboration beyond the measure itself, and none situates rasus within a broader legal framework or cites any case or statute in which the term appears outside of Fleta.
The anomalous fragment "Plunder;" appearing after the definition in Black's (2nd Ed.) is unexplained in that edition and is not reproduced in any other source surveyed here. It most likely represents a typographical or editorial error in the second edition's compilation — possibly the tail end of an adjacent entry that lost its headword. Researchers should not treat it as a recognized secondary meaning of rasus.
What the historical dictionaries collectively omit is any discussion of how the rasus fit into the broader system of medieval English commodity measurement, whether it was enforceable in particular courts, or how it related to similar measures for other agricultural goods. For that context, the Fleta itself and secondary scholarship on medieval English commercial law are the appropriate next resources.