- a girl brought up with another child of different parents.
Origin of foster sister
First recorded in 1640–50
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for foster sister
For the moment Dan forgot his complaint in the tender thought of his foster-sister.The Inn at the Red Oak
She drew her foster-sister away from Lennon with a grasp as resolute as it was gentle.
Yet she was no less mystified than Lennon by her foster-sister's manner.
Elsie struggled free from Lennon to fling her arms about her foster-sister.
Carmena checked her indignant protest and gazed down at her foster-sister.