With jack innanen, malik elassal, lucy freyer, amita rao. Created by ben kronengold, rebecca shaw. See examples of adult used in a sentence. A person who is fully grown or developed or of age. A person or animal that has grown to full size and strength: A twenty-something … In contrast to a non-adult or minor, a legal adult is a person who has attained the age of majority and is therefore regarded as independent, self … Being, involving, or relating…. The meaning of adult is fully developed and mature : How to use adult in a sentence.