Definition
In Roman law, the deunx (plural: deunces) is a fractional unit equal to eleven-twelfths of the as — the standard Roman unit of inheritance and property division. The as was divided into twelve equal parts called unciae, and named fractions corresponded to each combination of those parts. The deunx represents eleven of those twelve parts, leaving one uncia (one-twelfth) unaccounted for.
The term appears almost exclusively in the context of Roman inheritance law, where estates were notionally divided into twelve parts and distributed among heirs according to these named fractions. A testator could leave a deunx to one heir and an uncia to another, together constituting the whole as.
Why It Matters in Research
Researchers encounter deunx primarily when working with Roman law sources, civil law treatises, or English common law commentaries that trace property and inheritance concepts to Roman foundations. Blackstone references this fractional system in the second volume of his Commentaries, and civil law scholars writing on testamentary succession frequently enumerate the full duodecimal series.
The practical research trap is attempting to find deunx as a term of art in English common law cases or statutes — it has no such independent life. Its appearance in Black's and similar dictionaries reflects the strong Roman law foundation of Anglo-American legal scholarship rather than any operative use in English or American courts. If you are reading a primary source that uses deunx, you are almost certainly working with a Roman law text, a civil law jurisdiction document, or a scholarly commentary on either.
The full series of Roman fractional terms — uncia, sextans, quadrans, triens, quincunx, semis, septunx, bes, dodrans, dextans, deunx, as — appears as a set in treatises on Roman private law. Understanding the system as a whole is more useful than isolating any single term. When a source uses one of these terms, the others are likely nearby, and the researcher should approach the passage with the complete duodecimal framework in mind.
Historical Dictionary Support
Black's Law Dictionary defines deunx as a division of the as containing eleven unciae, equal to eleven-twelfths, citing Blackstone's Commentaries (2 Bl. Comm. 462, note). This is the standard treatment across historical legal dictionaries, which handle the Roman fractional inheritance terms as a cluster, each defined by reference to the as and to the relevant number of unciae.
Historical sources are consistent on the arithmetic and offer little divergence worth flagging. What they largely omit is any guidance on when and why a researcher in an Anglo-American legal context would encounter this term — they present it as taxonomic reference rather than as research intelligence. The term's presence in English-language legal dictionaries is essentially a legacy of the civil law training expected of serious legal scholars through the nineteenth century, when facility with Roman law terminology was considered foundational.