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a. Not fully grown or developed; young.
b. Of or characteristic of a young animal that has not reached sexual maturity: a bird still in juvenile plumage.
2. Characteristic of, intended for, or appropriate for children or young people: juvenile fashions.
3. Marked by immaturity; childish: juvenile behavior. See Synonyms at young.
4. Geology Relating to or being water, gas, or a mineral-rich fluid believed to have originated from magma and to have come to the earth's surface for the first time.
a. A young person; a child.
b. A young animal that has not reached sexual maturity.
c. A two-year-old racehorse.
2. An actor who plays roles of children or young persons.
3. A children's book.