late 15c., "admit or show one's knowledge," a blend of Middle English aknow "admit or show one's knowledge" and Middle English knowlechen "admit, acknowledge" (c. 1200; see knowledge). Middle English aknow is from Old English oncnawan "understand, come to recognize," from on (see on (prep.)) + cnawan "recognize;" see know).
"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: Acknowledged; acknowledging.
1580s, from un- (1) "not" + past participle of acknowledge (v.).
1590s, "act of acknowledging," from acknowledge + -ment. "An early instance of -ment added to an orig. Eng. vb." [OED]. Meaning "token of due recognition" is recorded from 1610s.
early 12c., cnawlece "acknowledgment of a superior, honor, worship;" for the first element see know (v.). The second element is obscure, perhaps from Scandinavian and cognate with the -lock "action, process," found in wedlock.
From late 14c. as "capacity for knowing, understanding; familiarity;" also "fact or condition of knowing, awareness of a fact;" also "news, notice, information; learning; organized body of facts or teachings." The sense of "sexual intercourse" is from c. 1400. Middle English also had a verb form, knoulechen "acknowledge" (c. 1200), later "find out about; recognize," and "to have sexual intercourse with" (c. 1300); compare acknowledge.
Since Knowledge is but sorrow's Spy,
It is not safe to know.
[Davenant, song from "The Just Italian," 1630]
*gnō-, Proto-Indo-European root meaning "to know."
It forms all or part of: acknowledge; acquaint; agnostic; anagnorisis; astrognosy; can (v.1) "have power to, be able;" cognition; cognizance; con (n.2) "study;" connoisseur; could; couth; cunning; diagnosis; ennoble; gnome; (n.2) "short, pithy statement of general truth;" gnomic; gnomon; gnosis; gnostic; Gnostic; ignoble; ignorant; ignore; incognito; ken (n.1) "cognizance, intellectual view;" kenning; kith; know; knowledge; narrate; narration; nobility; noble; notice; notify; notion; notorious; physiognomy; prognosis; quaint; recognize; reconnaissance; reconnoiter; uncouth; Zend.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit jna- "know;" Avestan zainti- "knowledge," Old Persian xšnasatiy "he shall know;" Old Church Slavonic znati "recognizes," Russian znat "to know;" Latin gnoscere "get to know," nobilis "known, famous, noble;" Greek gignōskein "to know," gnōtos "known," gnōsis "knowledge, inquiry;" Old Irish gnath "known;" German kennen "to know," Gothic kannjan "to make known."
"pertaining to confession," mid-15c., from Medieval Latin confessionalis, from past-participle stem of confiteri "to acknowledge" (see confess).
early 14c., professen, "to take a vow" (in a religious order), a back-formation from profession or else from Medieval Latin professare, from professus "avowed," literally "having declared publicly," past participle of Latin profiteri "declare openly, testify voluntarily, acknowledge, make public statement of," from pro- "forth" (from PIE root *per- (1) "forward") + fateri (past participle fassus) "acknowledge, confess" (akin to fari "to speak," from PIE root *bha- (2) "to speak, tell, say").
The meaning "declare openly" is recorded from 1520s, "a direct borrowing of the sense from Latin" [Barnhart]. Related: Professed; professing.