- a boy raised like one's own son, though not such by birth or adoption.
Origin of foster son
late Middle English word dating back to 1400–50
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for foster son
"I am Paris, the foster-son of Agelaus the herdsman," he answered.Children of the Dawn
Elsie Finnimore Buckley
Then it was not your foster-son's admiration of Cicero that caused his death?
If he does not teach him his handicraft, that foster-son may return to the house of his father.Archology and the Bible
George A. Barton
Heidreker was afterwards in Russia, and the son of the king was his foster-son.The Fairy Mythology
Biorn's foster-son is worth speaking about; what have you done with him?The Vinland Champions
Ottilie A. Liljencrantz