Definition
A Roman law term denoting an informal testamentary instrument of lesser force than a formal will (testamentum). The codicillus functioned as a supplement or alternative to a will, distinguished by its reduced formality requirements and limited operative scope. Unlike the testamentum, the codicillus could not directly institute or disinherit an heir; it could transfer property only through the mechanism of a trust (fideicommissum), by which the testator requested — rather than commanded — a named person to carry out a disposition. The instrument could be executed either before or after a formal will, and its validity was not dependent on observance of the ceremonial requirements that governed full testamentary documents.
Common Confusion
CODICILLUS vs. CODICIL: English-language legal dictionaries routinely treat codicillus as the direct Latin ancestor of the modern codicil, and the two are related in concept. They are not identical in operation. The modern codicil is a formal supplement to an existing will, subject to the same execution requirements as the will itself, and it can alter substantive provisions including appointments of heirs. The codicillus, by contrast, was defined partly by its inability to make direct dispositions of an inheritance — it achieved testamentary effect only indirectly through the fideicommissum. Researchers who treat the terms as interchangeable in historical sources risk misreading the operative limits of Roman-era instruments.
Why It Matters in Research
Codicillus appears almost exclusively in sources dealing with Roman law, civil law tradition, or comparative legal history. Researchers working in the Law Mind corpus should expect to encounter the term in three contexts: (1) treatises and commentaries tracing the development of testamentary law from Roman roots into civil law jurisdictions; (2) historical analyses of English equity, where fideicommissary reasoning influenced the development of trusts; and (3) glossaries and legal dictionaries from the eighteenth and nineteenth centuries that preserved Latin terminology as a matter of scholarly convention rather than practical usage.
A significant research trap: nineteenth-century American and English legal dictionaries frequently included codicillus as a headword alongside codicil, creating the appearance that both terms were in active legal use. In practice, codicillus had no operative role in common law systems. Its presence in dictionary entries is descriptive and historical, not prescriptive. A researcher citing a dictionary definition of codicillus in support of a proposition about codicil law in a common law jurisdiction is misusing the source.
The fideicommissum connection is the most substantively important feature for comparative law research. The codicillus's dependence on trust-like mechanisms to achieve testamentary effect is a window into how Roman law managed informality — a point of genuine doctrinal interest when tracing how beneficial ownership and equitable obligations developed in legal systems with civil law foundations.
Historical Dictionary Support
Black's Law Dictionary (both first and second editions) defines codicillus identically and minimally: "an informal and inferior kind of will, in use among the Romans." The entry functions as a cross-reference to codicil rather than a freestanding analysis.
Burrill's Law Dictionary is the most useful of the three sources. It preserves a Latin phrase — nullam solemnitatem ordinationis desiderant ("they require no solemnity of execution") — that directly identifies the instrument's defining characteristic. Burrill also notes the two-directional timing rule (the codicillus could precede or follow a formal will) and the inheritance limitation operating through trust. This is the entry to consult for substantive content; the Black's entries add nothing beyond identification.
What all three sources omit: none addresses the Augustan-era legal reforms that formally recognized the codicillus as a distinct instrument, nor do they discuss the requirement that a testator express an intention that the instrument be treated as a codicillus (rather than as a failed will) — a nuance with practical consequences in Roman jurisprudence that later civil law commentators analyzed at length.
Jurisdictional Note
Codicillus has no operative standing in common law jurisdictions. In civil law systems with Roman law foundations — particularly in the mixed jurisdictions of Louisiana, Quebec, and South Africa — historical understanding of the codicillus informs scholarly commentary on testamentary formality, though modern statutory frameworks govern actual practice.