Definition
As used in law, lunar means belonging to, measured by, or reckoned according to the revolutions of the moon. The term appears almost exclusively in legal texts in the compound form lunar month, where it functions as a modifier distinguishing one method of time measurement from others. A lunar month is the period from one new moon to the next, approximately 29.5 days. The practical legal significance of the word lies entirely in this calendrical context: when a statute, contract, or legal instrument specifies a period measured in months, the question of whether those months are lunar, calendar, or some other reckoning can materially affect the computation of deadlines, notice periods, and rights. See MONTH.
Common Language
Modern common usage (Wiktionary): Pertaining to the moon; of or relating to Earth's natural satellite.
Historical common usage (Webster's 1913): Of or pertaining to the moon; measured by the revolutions of the moon; influenced by the moon in growth or character. Also used in scientific and alchemical compounds such as lunar caustic (silver nitrate).
The gap between common and legal meaning is narrow but worth flagging. In ordinary English, lunar carries broad descriptive meaning — anything moon-related qualifies. In legal usage, the word is almost entirely stripped of its general descriptive function and appears only in the specific technical context of time measurement. A legal researcher encountering lunar should immediately read it as shorthand for a question about month computation, not as a general astronomical or descriptive term.
Common Confusion
Lunar month, calendar month, and solar month are not interchangeable, though older statutes and instruments sometimes left the type of month unspecified and courts were left to determine which method applied. A lunar month runs approximately 29 days, 12 hours — shorter than a standard calendar month of 30 or 31 days and shorter than a solar year divided by twelve (approximately 30.44 days). When a legal instrument says "month" without qualification, most modern jurisdictions default to the calendar month. Assuming that an unqualified "month" means a lunar month in older documents is a common interpretive error. Researchers should also avoid conflating lunar month with the now-archaic legal month of four weeks (28 days), which was a distinct common law convention.
Why It Matters in Research
The practical research stakes for this term are almost entirely chronological and computational. In older English statutes, common law pleading rules, and pre-modern instruments, lunar months were sometimes the operative unit of time. When reading 18th- or 19th-century legal materials, a reference to a month may silently mean a lunar month — particularly in contexts involving ecclesiastical law, admiralty, or agricultural tenancies, where lunar reckoning had deeper historical roots. Misreading the intended unit can throw off deadline calculations by several days per period, which compounds over multiple intervals.
The term appears in Law Mind corpus materials primarily as a cross-reference anchor. Historical dictionaries almost universally redirect the reader to MONTH for substantive treatment, so researchers who encounter lunar in a source index or term list should follow that cross-reference rather than treating the lunar entry itself as self-contained. The entries in Black's and Bouvier's are definitional placeholders, not substantive analyses.
Jurisdictional variation in the treatment of month computation adds another layer. English common law treated the legal month as four weeks (28 days) in some contexts, while American courts generally moved toward the calendar month earlier. A document governed by English law from a period when lunar or four-week months were operative requires different computation than a similar American document from the same era.
Historical Dictionary Support
The four source dictionaries are in complete agreement and offer minimal independent analysis. Black's (both editions), Anderson's, and Bouvier's all define lunar identically — belonging to or measured by the revolutions of the moon — and all redirect substantive discussion to the entry for MONTH. None of them elaborate on the legal significance of lunar time reckoning beyond that redirect, which itself signals that the term's legal weight was considered self-evident to contemporary practitioners.
Black's 2nd Edition includes a transitional passage moving from lunar month directly into the LUNATIC entry, suggesting the editorial view that lunar as a standalone term required no more than a brief definitional sentence. Bouvier's is characteristically spare. Anderson's simply cross-references MONTH with no additional content.
What the historical dictionaries miss: they do not address the interpretive problems that arise when older instruments specify lunar months and later courts must apply them — a gap that became practically significant as calendar-month conventions became dominant.
Jurisdictional Note
In most modern common law jurisdictions, statutory and contractual references to months default to calendar months absent explicit contrary specification. Instruments expressly specifying lunar months are rare in contemporary practice but appear in older recorded documents that remain legally operative, particularly in property and ecclesiastical contexts. Researchers working with English ecclesiastical or pre-1900 admiralty materials should be alert to lunar month as the operative standard.