n. The act of adopting or taking as one's own; a choosing for use, or by way of preference or approval; assumption; formal acceptance: as, the adoption of a distinctive dress; he favored the adoption of the bill; the adoption of a new word into a language.n. The act of taking into an affiliated relation; admission to some or all of the privileges of natural kinship or membership: as, the adoption of a child; adoption into a tribe; a son by adoption.n. In theology, that act of divine grace by which, through Christ, those who have been justified “are taken into the number and enjoy the liberties and privileges of the children of God.”