Definition
A Latin adjective meaning "sound" or "healthy," used in historical legal contexts primarily in reference to mental soundness. SANUS appears most often as a component of the phrase SANA MENS or SANAE MENTIS (sound mind), which formed part of the standard language used to attest a testator's mental capacity in wills and probate proceedings. Standing alone, the term simply supplies the adjectival root that anchors those compound expressions.
Common Language
Modern common usage (Wiktionary): No direct English entry; listed only as a plural form of "sanu," a word in certain other languages. The term has no active life in ordinary English.
Historical common usage (Webster's 1913): Not listed as an English word; recognized only as a Latin root underlying English derivatives such as "sane," "sanity," and "sanitary."
The gap worth noting: English legal writers borrowed SANUS directly from Latin without anglicizing it, which means researchers encountering the word in historical documents must treat it as a technical Latin legal term, not as an English word that merely looks unfamiliar. Its meaning is carried forward into modern practice through derived English terms — "sane," "sanity," "sound mind" — but the Latin form itself signals a document of some age or formality.
Common Confusion
SANUS is routinely encountered only as a fragment of longer Latin phrases and is seldom indexed independently. Researchers sometimes search for SANUS and miss the substantive discussion, which appears under SANA MENTIS, SANAE MENTIS, or COMPOS MENTIS in historical dictionaries and treatises. These are not synonyms in all respects: COMPOS MENTIS (literally "master of one's mind") carries a slightly broader common-law usage and appears more frequently in judicial opinions, while SANA MENTIS is more characteristic of civil-law and ecclesiastical contexts, including will formulas. Do not assume that finding one phrase exhausts the relevant sources on mental soundness.
Why It Matters in Research
Researchers working in the Law Mind corpus will encounter SANUS almost exclusively in one of two settings: (1) as the root term cross-referenced from SANA MENTIS or SANAE MENTIS entries in historical dictionaries, or (2) embedded in Latin maxims and will clauses reproduced in treatises on testamentary capacity, probate, and guardianship.
The practical trap is indexing. Historical dictionaries, including Burrill's, often place the substantive discussion under the genitive or ablative form of the word (MENTIS SANAE, SANAE MENTIS) rather than under SANUS itself. A researcher who searches only under the nominative form will surface a brief cross-reference — exactly as Burrill's provides — and may conclude the corpus has little to say on mental capacity. The real material is elsewhere.
The term also appears at the edge of the maxim Sapiens incipit a fine — quoted in Burrill's entry — which concerns the relationship between intention and execution. That maxim has independent relevance to contract and testamentary interpretation and should be tracked separately from the mental-soundness material with which Burrill incidentally groups it.
For historical documents: wills drafted before the mid-nineteenth century, particularly those with ecclesiastical probate origins, frequently recite that the testator was "sanus mentis et memoria" or a close variant. Identifying this formula is essential to understanding the legal standard being invoked and the jurisdiction's requirements at the time of execution.
Historical Dictionary Support
Burrill's Law Dictionary gives only a brief cross-reference entry: "Lat. Sound. See Sana mentis." This is consistent with the term's function — it is a root, not a doctrine. Burrill's does not define the mental-capacity standard under SANUS itself, directing the reader instead to the compound phrase where the substantive analysis lives.
What historical dictionaries collectively miss: none of the standard historical dictionaries treat SANUS as a term of art in its own right. The word's legal significance is entirely derivative — it matters because of the phrases it forms. Researchers should therefore treat any historical dictionary entry for SANUS as an index pointer, not as a self-contained definition. The doctrinal content on mental soundness, testamentary capacity, and related guardianship standards must be assembled from the compound-phrase entries and from treatise discussions of those doctrines.
Jurisdictional Note
The underlying concept — mental soundness as a prerequisite to testamentary and contractual capacity — is universal across common-law and civil-law systems, but the specific Latin formula varies by jurisdiction and period. Civil-law jurisdictions and ecclesiastical courts favored SANAE MENTIS; common-law courts more consistently used COMPOS MENTIS. Researchers working across jurisdictions should search both formulations.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Testamentary Capacity; Mental Competency; Compos Mentis.