noun
only child; precious only child
Idiomatic expression for a family's sole child, often with a nuance of being cherished or precious. Literally 'one-grain seed'.
彼女は一粒種だから、両親に大事に育てられた。
She is an only child, so she was raised with great care by her parents.
一
Their precious only son went to study abroad, and the house became quiet.