An only child; a child with no siblings.
彼は一人っ子だから、家族の期待が大きい。
Because he is an only child, his family's expectations are high.
一人っ子の育て方について本を読んだ。
I read a book about how to raise an only child.
妹は一人っ子ではないが、実家ではよく甘やかされて育った。
My younger sister is not an only child, but she was often spoiled growing up at home.
一人っ子同士の結婚では、相続や介護の話がよく話題になる。
In marriages between only children, inheritance and caregiving often become topics of discussion.