Definition
Latin: "a month." In civil law and old English law, mensis denotes a calendar month as a unit of legal time measurement. The term appears primarily in Latin maxims, digest references, and archaic legal instruments where temporal calculations governed rights, obligations, or prohibitions. It carries no independent legal doctrine of its own but functions as a chronological building block within rules that depend on monthly reckoning.
The compound form mensis vetitus — the "prohibited month" or fence-month — had specific operational significance in English forest law, designating a period of roughly fifteen days before and after midsummer during which deer were protected from hunting while fawning. This application gave mensis its most consequential independent use in the English legal tradition.
Common Language
Modern common usage (Wiktionary): Mensis is the Latin word for "month," surviving in modern English primarily through derivatives such as "mensal," "semester," and medical terminology relating to monthly cycles.
Historical common usage (Webster's 1913): Webster's 1913 does not carry a standalone entry for mensis, treating it as a Latin root rather than an English word. Its English descendants — including "menstrual" and "trimester" — are defined through their biological or calendrical senses without legal content.
The gap between common and legal usage is minimal in one direction and precise in another. Mensis as a raw chronological term maps cleanly onto the ordinary sense of "month." Its legal specificity emerges not from any departure in meaning but from its deployment within formal Latin rules about time computation — where, for instance, the question of whether a month is counted inclusively or exclusively, by calendar days or by thirty-day periods, could determine the validity of a notice, plea, or prohibition.
Common Confusion
Mensis is sometimes encountered by researchers who confuse it with mensura (measure or standard of measurement) or conflate the fence-month prohibition with the broader concept of a close season. The fence-month was a legally defined interval with fixed boundaries in forest law; a close season is a more general regulatory concept that varies by statute, jurisdiction, and species. The two are related in purpose but distinct in origin and legal operation.
Why It Matters in Research
Researchers encounter mensis most often in three contexts: (1) civil law digests and their English translations, where monthly time periods govern procedural deadlines or obligations; (2) old English forest law materials, where mensis vetitus (fence-month) appears in royal grants, forest charters, and cases concerning hunting rights; and (3) Latin-language instruments generally, where temporal terms require translation before legal effect can be assessed.
The principal research trap is the month-computation problem. Roman law and early English law did not always count months the same way modern law does. A mensis in a Roman text may be computed from a specific day of one month to the corresponding day of the next, while English common law instruments sometimes treated a month as a fixed thirty-day period regardless of the calendar. When a document's validity or a right's duration turns on the length of a month, the applicable computation rule must be identified before the term mensis can be mechanically translated.
For fence-month research specifically, the relevant corpus is forest law: royal forest charters, eyres of the forest, and treatises on forest custom. The fence-month prohibition was a crown prerogative matter and appears in administrative rather than common-law records. Researchers tracing hunting rights, poaching prosecutions, or forest tenure will find mensis vetitus embedded in the Latin texts of those sources; cross-referencing to FENCE-MONTH in this dictionary is essential before drawing conclusions about the scope or duration of the prohibition.
Historical Dictionary Support
The three source dictionaries — Black's (1st ed.), Black's (2nd ed.), and Burrill's — are in complete agreement on both the base definition and the compound form. All three define mensis as "a month" in civil and old English law, and all three cross-reference mensis vetitus to fence-month. The entries are nearly identical; neither Black's edition adds substantive content beyond Burrill's, and Burrill's provides the only additional scholarly anchor, citing Digest 50.17.101 — a genuine locus in Justinian's Digest dealing with rules of general application, where monthly computation appears in the context of legal maxims about time.
What the historical dictionaries do not address: none of the three sources discusses the computation problem — whether a mensis is a calendar month, a thirty-day month, or some other interval. This omission is significant for practical research. A researcher who stops at the dictionary definition has confirmed the translation but has not resolved the operative legal question. The Digest citation in Burrill's points toward civil law sources that do address computation, but the dictionaries themselves leave the researcher to pursue that question independently.
Jurisdictional Note
As a Latin term of art, mensis has no distinct modern American or English jurisdictional application. Its legal significance is historical and is therefore bounded by the era and legal system in which the relevant instrument or text was produced — principally Roman civil law and English law prior to the nineteenth century.