confirmation (n.)

c. 1300, confyrmacyoun, the rite whereby baptized persons are admitted to full communion with the Church, from Old French confirmacion (13c.) "strengthening, confirmation; proof; ratification," and directly from Latin confirmationem (nominative confirmatio) "a securing, establishing; an assurance, encouragement," noun of action from past-participle stem of confirmare (see confirm).

Meaning "verification, proof, supporting evidence" is from late 14c. Meaning "act of rendering valid by formal assent of authority" is from c. 1400; sense of "action of making sure, a rendering certain or proving to be true" from early 15c.