acknowledge (v.)

late 15c., “admit or show one’s knowledge,” a blend of Middle English aknow “admit or show one’s knowledge” (from Old English oncnawan “understand, come to recognize,” from on (see on (prep.)) + cnawan “recognize;” see know) and Middle English knowlechen “admit, acknowledge” (c. 1200; see knowledge). “By 16th c. the earlier vbs. knowledge and a(c)know … were obs., and acknowledge took their place” [OED].

In the merger, an unetymological -c- slipped in; perhaps the explanation is that when English kn- became a simple “n” sound, the -c- stepped up to preserve, in this word, the ancient “kn-” sound. Related: Acknowledgedacknowledging.

recognition (n.)

mid-15c., “knowledge of an event or incident; understanding,” from Middle French recognition (15c.) and directly from Latin recognitionem (nominative recognitio) “a reviewing, investigation, examination,” noun of action from past participle stem of recognoscere “to acknowledge, know again; examine” (see recognize).

Sense of “formal avowal of knowledge and approval” is from 1590s; especially acknowledgement of the independence of a country by a state formerly exercising sovereignty (1824). Meaning “a knowing again” is from 1798

apostille

n.A special sign established in 1961 for certifying foreign documents.

Noun. apostil (plural apostils) A marginal note; a gloss. A method of verification for international documents. The deponent’s signature was verified in accordance with the apostil to the Hague convention.