Definition
A Latin term meaning "one" or "the same," used in legal contexts to indicate singularity, unity, or simultaneity of action. UNUS appears most often as a component of longer Latin phrases that carry distinct legal meanings, including:
1. UNO ACTO — In one act; by the same act. Used to describe actions or legal consequences that occur simultaneously or as part of a single transaction, without intervening steps.
2. UNO FLATU — In one breath; in the same utterance. Used to describe statements or acts performed in a single, continuous expression, often in contexts involving the delivery of instruments, the pronouncement of judgment, or the construction of simultaneous declarations.
3. UNA VOCE — With one voice; unanimously. Used to characterize decisions, verdicts, or resolutions made without dissent.
UNUS does not typically appear as a freestanding legal term. Its significance in legal discourse is almost entirely as the root or first element of these compound Latin phrases.
Common Language
Wiktionary: "unus" — The Latin word for "one," the cardinal number. Also used in modern Romance languages as a root for words meaning one or unity.
Webster's 1913: Not separately defined, but acknowledged as the Latin root underlying English derivatives such as "unit," "union," and "unanimous."
The gap here is one of context rather than meaning. The common meaning is straightforwardly numerical. In legal usage, UNUS carries a procedural or analytical weight — the unity or simultaneity it signals can determine whether a legal act is valid, whether liability attaches, or whether a statement is admissible as a single utterance.
Why It Matters in Research
Researchers encountering UNUS in historical legal texts will almost never find it standing alone. The term functions as a building block, and its legal significance is carried entirely by the phrase in which it appears. When reading older English equity or common law sources, Latin compound phrases built on UNUS signal precision about timing and unity — distinctions that mattered considerably in formal pleading and the execution of legal instruments.
UNO ACTO is the most practically significant construction. Courts used it to analyze whether two legal consequences arose from a single act (which could affect questions of merger, election of remedies, or simultaneous conveyances). UNO FLATU similarly appeared in debates about whether a testator, grantor, or speaker had made a single coherent declaration or two separate ones — a distinction with real consequences for instrument construction.
Researchers working in ecclesiastical law, civil law traditions, or Scottish law sources may encounter UNUS and its compounds more frequently than in English common law materials, where Latin was progressively displaced. American legal sources after the mid-nineteenth century rarely use these phrases, so their appearance in a document can itself be a dating or provenance signal.
Be alert to the fact that older indexes and digests may not index UNO ACTO or UNO FLATU as standalone headings; researchers may need to search under the substantive doctrines those phrases describe (e.g., simultaneous acts, unity of transaction, contemporaneous construction) rather than under the Latin.
Historical Dictionary Support
Anderson's Dictionary of Law is the sole shelf source providing a definition for this term, and its treatment is appropriately compact: it glosses UNUS as "one; the same" and immediately pivots to defining its compound forms, UNO ACTO and UNO FLATU, as well as UNA VOCE. This reflects the practical reality that UNUS was not a term courts or practitioners deployed in isolation. Anderson's entry is accurate as far as it goes but offers no doctrinal context for when these phrases were invoked or what legal consequences followed.
No other Law Mind historical dictionary sources address UNUS directly, which is itself informative. The term's presence in legal Latin glossaries is largely inherited from civilian (Roman and canon law) tradition. Bouvier's Law Dictionary, notably, does not appear to give UNUS a dedicated entry, treating its compounds only incidentally.