What is Arrogation?

Legal Definition
Civil law. Signifies nearly the same as adoption; the only difference between them is this, that adoption was of a person under full age but as arrogation required the person arrogated, sui juris, no one could be arrogated till he was of full age. Dig. 1, 7, 5; Inst. 1, 11, 3 1 Brown's Civ. Law, 119.
-- Bouviers Law Dictionary
Legal Definition
In the civil law. The adoption of a person who was of full age or sui juris. 1 Browne, Civil & Adm. Law, 119; Dig. 1, 7, 5; Inst. 1, 11, 3. Reinders v. Kop-pelmann, 68 Mo. 497, 30 Am. Rep. 802.
-- Black's Law Dictionary
Legal Definition
Adoption of one sui juris.
-- Ballentine's Law Dictionary