adult
Americannoun
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a person who is fully grown or developed or of age.
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a full-grown animal or plant.
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a person who has attained the age of maturity as specified by law.
adjective
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having attained full size and strength; grown up; mature.
an adult person, animal, or plant.
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of, relating to, or befitting adults.
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intended for adults; not suitable for children.
adult entertainment.
verb (used without object)
adjective
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having reached maturity; fully developed
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of or intended for mature people
adult education
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regarded as suitable only for adults, because of being pornographic
adult films and magazines
noun
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a person who has attained maturity; a grownup
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a mature fully grown animal or plant
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law a person who has attained the age of legal majority (18 years for most purposes) Compare infant
Usage
What does adult mean? An adult is a person who is fully grown or developed. This could refer to a person’s body being done growing or their mind being fully developed. An adult child is someone’s child who is fully grown, as in Murray’s adult children are all married and have children of their own. An adult is also a person who has reached an age that their society says allows them responsibilities and benefits not allowed to children. For example, in the United States someone who is 18 years old is in many cases considered an adult. Eighteen-year-olds can vote, sign a contract, join the military, and other actions children are not allowed to do. An adult can also be a fully grown or matured plant or animal, as in Once my puppy becomes an adult, I’ll need to get them a bigger crate. Adult can also be used to describe something related to adults or adulthood, such as adult responsibilities—like paying rent. Adult can also be used to describe something not suitable for children. Things labeled as adult entertainment, for example, often include explicit sexual content. Informally, adult can be used as a verb meaning to take on responsibilities usually reserved for adults, such as owning a house. It’s often used humorously to describe small responsibilities, as in Tanya really adulted today by putting away her laundry.
Other Word Forms
Etymology
Origin of adult
First recorded in 1525–35; from Latin adultus “grown” (past participle of adolēre “to make grow”), equivalent to ad- ad- + ul- (identical with base al- in aliment ( def. ) ) + -tus past participle suffix
Explanation
Adult is noun and an adjective, both of which refer to something mature, no longer a child. A full-grown person is called an adult: they can vote, rent cars, and choose to eat sugary cereal for dinner every night. If you're still a child, then you are not an adult — that's the noun version. Childish people don't behave in an adult manner — that's the adjective. A child might be scared by the Wicked Witch of the West, but an adult knows she's not real. Learning the difference between real life and make-believe is one of the upsides of becoming an adult.
Vocabulary lists containing adult
Common Five-letter Words for Wordle, List 1
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Growth, Development and Reproduction of Organisms - Middle School
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Growth, Development and Reproduction of Organisms - Introductory
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Adult liver cells divide much less frequently, giving them more time to repair damage before it becomes harmful.
From Science Daily • Apr. 29, 2026
Adult social care accounted for about 40% of net service spend by the English councils responsible for it in 2024-25, according to BBC analysis of government figures.
From BBC • Apr. 28, 2026
It was a post-#MeToo law, the Adult Survivors Act, that allowed the journalist and advice columnist E. Jean Carroll to bring her civil sexual abuse case against Trump.
From Salon • Apr. 19, 2026
The Center for Baby and Adult Hygiene Products, the trade association representing diaper manufacturers, opposes the bill.
From Los Angeles Times • Apr. 10, 2026
The walls of the Young Adult Room were painted purple and yellow.
From "Escape from Mr. Lemoncello's Library" by Chris Grabenstein
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
