Only Child

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A child with no siblings, either biological or adopted. Despite years of research, large amounts of data and opposing theories, there is little evidence to suggest that only children are maladjusted.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
References in classic literature ?
Luther, according to the scandal of his monkish enemies, was a brat of that hellish breed; nor was Pearl the only child to whom this inauspicious origin was assigned among the New England Puritans.
They devoured my little daughter, my child, my only child! I have no longer any heart, they devoured it!"
At the only child seat checkup Alexandria held in 1997, they checked 71 restraints.
I had a lot of problems as an only child, a child whose parents were divorced at a time when divorce was very rare, and this made me a particular oddity.
"It's very difficult for children to be the only child of color in a class," Griffin points out.