The Collaborative International Dictionary of English v.0.48:

Adrogation \Ad`ro*ga"tion\, n. [L. adrogatio, arrogatio, fr.
   adrogare. See Arrogate.] (Rom. Law)
   A kind of adoption in ancient Rome. See Arrogation.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

ADROGATION, 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.