Definition
A person who has attained the legally recognized age of majority and is therefore vested with full legal capacity to contract, sue, vote, and otherwise act in their own right without the intervention of a guardian or next friend.
The precise age threshold has never been uniform across legal systems or time periods. Under traditional common law, an adult was a person who had reached the age of twenty-one, regardless of sex. Under Roman and civil law, the threshold was lower and was sex-differentiated: males became adults at fourteen, females at twelve — ages tied to presumed physical puberty rather than civil maturity. In modern American law, the operative age in most jurisdictions is eighteen, following statutory reform beginning in the 1970s, though twenty-one remains the threshold for certain regulated purposes (alcohol purchase, handgun acquisition under federal law). The word functions as a legal status, not merely a biological description.
Common Language
Modern common usage (Wiktionary): An animal that is full-grown; a person who has reached the legal age of majority.
Historical common usage (Webster's 1913): Having arrived at maturity, or to full size and strength; matured — as in an adult person, plant, or animal.
The common meaning tracks biology: an adult is simply a mature organism. The legal meaning tracks status and capacity. The gap matters because legal adulthood is a fixed threshold set by positive law, not a judgment about individual maturity. A seventeen-year-old may be physically and intellectually mature; they remain a minor in law. Conversely, reaching the statutory age confers adult legal status automatically, without any inquiry into actual development.
Common Confusion
Two distinct thresholds operate under the label "adult" simultaneously in many legal systems: the age of majority (conferring general civil capacity) and specific regulatory ages (alcohol, tobacco, gambling, firearms). A person may be an adult for purposes of contract and criminal liability while remaining a legal minor for other regulated activities. Historical sources compound the confusion by carrying forward the civil-law standard (fourteen/twelve) alongside the common-law standard (twenty-one) without always flagging which system governed the transaction or statute under analysis.
Recognized Forms
/SUBTYPES
Age of majority (general): The threshold at which a person acquires full civil and legal capacity. Currently eighteen in most U.S. jurisdictions by statute.
Regulatory adult: A person old enough to engage in a specific regulated activity, which may be set higher or lower than the general age of majority depending on the subject matter.
Adult for criminal purposes: In the context of juvenile justice, the age at which an offender is processed in adult criminal court rather than juvenile court. This may be set by statute below the general age of majority in some jurisdictions, or reached earlier through judicial waiver or prosecutorial transfer.
Why It Matters in Research
Threshold shifts over time are a primary trap. Pre-1970s primary sources — cases, statutes, treatises — nearly always set adulthood at twenty-one. Researchers reading nineteenth- or early twentieth-century materials must not assume that the modern eighteen-year threshold applied. A contract case holding that a party lacked capacity may rest entirely on an age standard no longer in force.
The civil-law / common-law split in historical dictionaries is not academic. American jurisdictions with civil-law heritage (Louisiana, and to varying degrees Texas and other former Spanish territories) may have absorbed the Roman-derived threshold in early decisions. Black's 2nd Edition explicitly notes that some states treated women as adults at eighteen even when twenty-one remained the general standard — a gender-differentiated rule now abolished but present in older authorities.
Context dependency is significant when searching the corpus. "Adult" in a probate or guardianship context, a criminal sentencing context, a contract capacity context, and a family law (adoption, custody) context may invoke different statutory definitions within the same jurisdiction and the same era. Always identify the governing statute's definition rather than relying on the dictionary standard.
For juvenile transfer research specifically, the operative question is not chronological age alone but the statutory mechanism — automatic exclusion, prosecutorial direct file, or judicial waiver — each of which treats "adult" as a legal destination rather than a fixed age.
Historical Dictionary Support
The five source dictionaries agree on the core civil-law / common-law divide and trace it to the same authority: Domat (Liv. Prel. tit. 2, § 2, n. 8) for the civil-law standard, and Swanston's Chancery Reports (533/553) for the common-law standard of twenty-one. The quotation preserved in Black's 1st Edition — "the authorities all agree, so far as we are advised, that at common law the word 'adult' signifies a person who has attained the full age of 21 years" — captures the pre-reform consensus accurately.
Burrill adds the useful gloss that the civil-law designation tracked the concept of adolescentia, linking adult status to a recognized developmental stage rather than an arbitrary number. This explains why the Roman threshold was sex-differentiated: the underlying theory was biological, not civic.
What the historical dictionaries miss almost entirely is the statutory reform wave of the late twentieth century. None of these sources anticipates the near-universal shift to eighteen as the age of majority. Researchers should treat all dictionary entries from Bouvier, Burrill, Anderson, and both Black's editions as reflecting pre-reform law. The 2nd Edition of Black's gestures toward variation ("though in some states women are legally 'adults' at 18") but does not signal how comprehensive the change would become.
Anderson's entry is notably the most practical of the five, embedding the term in a specific statutory context (aggravated assault) and noting what proof is required in adjacent matters — a reminder that dictionaries of this era often defined legal terms by reference to the disputes in which they appeared rather than as abstract concepts.
Jurisdictional Note
Most U.S. states set the general age of majority at eighteen by statute, following the Twenty-Sixth Amendment's influence and parallel legislative reform in the early 1970s. Louisiana retains some civil-law influences in its private law framework but follows the eighteen-year threshold for majority. Federal law applies its own age definitions by subject matter — eighteen for voting and general majority purposes, twenty-one for alcohol — and these do not displace state definitions in areas of state competence.
Encyclopedia Cross-Reference
Adoption — Adult Adoption (The Law Mind Family Law Encyclopedia)
Juvenile Transfer / Waiver to Adult Court (The Law Mind Criminal Law Encyclopedia)
Guardianship of Incapacitated Adults — Overview and Standards (The Law Mind Family Law Encyclopedia)