What does adult mean?
An adult is a human being who has reached full physical, mental, and legal maturity, most commonly defined by law as someone aged eighteen or older. The term functions both as a noun, referring to such a person, and as an adjective describing things intended for or characteristic of grown-ups — an adult education class, an adult size, or adult content. Beyond its legal sense, 'adult' often carries connotations of responsibility, level-headedness, and emotional maturity: to behave 'like an adult' is to act with restraint and good judgment rather than impulsiveness. The word derives from the Latin 'adultus', the past participle of 'adolescere', meaning 'to grow up', making it etymologically linked to 'adolescent'. Its derivatives include 'adulthood', denoting the state or period of being grown up. Widely used in law, medicine, education, and everyday speech, 'adult' is a foundational term for distinguishing the mature from the immature across social, legal, and biological contexts.
A person who has attained full growth and legal maturity, typically aged eighteen or over.
"Tickets cost £15 for adults and £8 for children."
In legal contexts, the age threshold varies slightly by jurisdiction and purpose (e.g., voting, drinking, criminal responsibility).
Relating to, intended for, or characteristic of fully grown people; also, showing mature judgment or responsibility.
"The film contains adult themes and is not suitable for young viewers."
Regular plural formation; used when referring to multiple grown persons, e.g., in pricing, statistics, or group descriptions.
"The survey included over 2,000 adults aged between 25 and 54."
The word 'adult' comes from the Latin 'adultus', meaning 'grown up' — literally the past participle of 'adolescere', to grow up. So every time you say you're adulting, you're using a word that's been growing for two thousand years.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of adult
The word 'adult' entered English in the early 16th century, borrowed from the Latin 'adultus', meaning 'grown up' or 'mature'. This is the past participle of 'adolescere', a verb formed from 'alere' ('to nourish') with the intensive prefix 'ad-', giving the sense of 'growing to full size'. It shares this root with 'adolescent', which refers to one still in the process of growing up, and more distantly with words like 'coalesce' and 'senescence', all tracing back to the same Proto-Indo-European root *al- meaning 'to grow or nourish'.
Related word forms
How adult is actually used
As a noun, 'adult' is neutral in register and used across formal and informal contexts. The phrase 'adulting' emerged in 21st-century informal usage to describe performing mundane adult responsibilities like paying bills or doing laundry, often with a self-aware or humorous tone. In British English, both /ˈædʌlt/ and /əˈdʌlt/ are heard; US English tends to favour /əˈdʌlt/. The adjective sense implying mature behaviour ('be an adult about this') carries a mildly prescriptive connotation.
Easily confused with adult
An adolescent is a teenager in the process of maturing (roughly ages 10–19), whereas an adult has reached full maturity.
Despite sharing a Latin root meaning 'to grow', 'adulterate' means to make something impure or inferior by adding another substance.