What is Adrogation?

Legal Definition
Adrogation, among ancient Romans, was a kind of adoption in which the person adopted was free, and consented to be adopted by another. It was done at the assembly of the people while the commonwealth subsisted, and later by a rescript of the emperors.

This is contrasted with arrogation, in which one claims another for oneself without the right.
-- Wikipedia
Legal Definition
Civil law. The adoption of one who was impubes, that is, if a male, under fourteen years of age; if a female, under twelve. Dig. 1, 7, 17, 1.
-- Bouviers Law Dictionary
Legal Definition
In the civil law. The adoption of one who was impubes; that is. If a male, under fourteen years of age; if a female, under twelve. Dig. 1, 7, 17, 1.
-- Black's Law Dictionary
Legal Definition
A Roman law adoption of one who has net reached the age of puberty.
-- Ballentine's Law Dictionary