adult

American  

[uh-duhlt, ad-uhlt] / əˈdʌlt, ˈæd ʌlt /

noun

1. a person who is fully grown or developed or of age.

2. a full-grown animal or plant.

3. a person who has attained the age of maturity as specified by law.

---

adjective

1. having attained full size and strength; grown up; mature.

   an adult person, animal, or plant.

2. of, relating to, or befitting adults.

3. intended for adults; not suitable for children.

   adult entertainment.

verb (used without object)

1. Informal. (of a young person) to do things and assume responsibilities that are associated with being an adult; act like an adult (usually used facetiously about minor accomplishments).

   I cook dinner for myself most nights—guess that means I'm adulting.

adult British  

/ ˈædʌlt, əˈdʌlt /

adjective

1. having reached maturity; fully developed

2. of or intended for mature people

   adult education

3. regarded as suitable only for adults, because of being pornographic

   adult films and magazines

---

noun

1. a person who has attained maturity; a grownup

2. a mature fully grown animal or plant

3. 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

• adulthood noun
• adultlike adjective
• adultly adverb
• adultness noun
• nonadult adjective
• quasi-adult adjective
• subadult adjective
• subadultness noun
• unadult adjective

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

Example Sentences

At the same time, the therapy also produced meaningful improvements in adult patients.

From Science Daily • Apr. 3, 2026

"The teenagers said they had been pressured by the adult," another source close to the case added.

From Barron's • Apr. 1, 2026

The 68-year-old was looking after two adult dogs, eight puppies and a child while Warren, an amateur rapper, was filming a music video in London.

From BBC • Mar. 31, 2026

“Each of the complainants was a highly educated adult with access to outside resources, social networks, and the unfettered ability to leave the community at any time,” wrote her lawyer, Jennifer Bonjean.

From The Wall Street Journal • Mar. 30, 2026

“We’re minors without adult supervision. Can’t they bring us meals and send someone to keep us entertained until Mom comes back? That’s what the Guardian force would do if we weren’t considered fugitives.”

From "The Manifestor Prophecy" by Angie Thomas

Related Words

• man
• person
• woman