in Latin, the form of com- "together, with" in compounds with stems beginning in vowels, h-, and gn-; see com-. Taken in English from 17c. as a living prefix meaning "together, mutually, in common," and used promiscuously with native words (co-worker) and Latin-derived words not beginning with vowels (codependent), including some already having it (co-conspirator).

*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."

early 13c., "make oneself known" (reflexive, now obsolete); early 14c., "to gain for oneself personal knowledge of," from Old French acointer "make known; make or seek acquaintance of," from Vulgar Latin *accognitare "to make known," from Latin accognitus "acquainted with," past participle of accognoscere "know well," from ad "to" (see ad-) + cognitus, past participle of cognoscere "come to know" (see cognizance).

Meaning "to inform (someone of something), furnish with knowledge or information" is from 1550s. Related: Acquainted; acquainting.

1670s, "capable of being known," also "liable to be tried in a given court or jurisdiction," from stem of cognizance (q.v.) + -able. Related: Cognizably; cognizability.

"having knowledge;" in law, "competent to take legal or judicial notice," 1744, back-formation from cognizance.

"perceive, become conscious of," 1650s, back-formation from cognizance. The French word is connaître (Old French conoistre). Related: Cognized; cognizing.

mid-15c., "heraldic mark;" 1530s, "knowledge, act or state of knowing," abstract noun from the past-participle stem of Latin cognoscere "to get to know, recognize" (see cognizance, which is now the usual word).

"foreknowledge," mid-15c., precognicioun, from Late Latin praecognitionem (nom. praecognitio) "foreknowledge," noun of action from past-participle stem of Latin praecognoscere "to foreknow," from prae "before" (see pre-) + cognoscere "to get to know, recognize" (see cognizance).