Etymology
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cogent (adj.)

"compelling assent or conviction," 1650s, from French cogent "necessary, urgent" (14c.), from Latin cogentem (nominative cogens), present participle of cogere "to curdle; to compel; to collect," literally "to drive together," from assimilated form of com "together" (see co-) + agere "to set in motion, drive, drive forward; to do, perform" (from PIE root *ag- "to drive, draw out or forth, move"). Related: Cogently.

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cognoscente (n.)

"connoisseur," 1778 (in the plural cognoscenti), an Italian word in English, re-Latinized in Italian from earlier conoscente "connoisseur," literally "knowing man," from Latin cognoscentum (nominative cognoscens), present participle of cognoscere "to get to know, recognize," from assimilated form of com "together" (see co-) + gnoscere "to know" (from PIE root *gno- "to know").

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cognitive (adv.)

1580s, "pertaining to cognition," with -ive + Latin cognit-, past participle stem of cognoscere "to get to know, recognize," from assimilated form of com "together" (see co-) + gnoscere "to know" (from PIE root *gno- "to know").

Taken over by psychologists and sociologists after c. 1940. Cognitive dissonance "psychological distress cause by holding contradictory beliefs or values" (1957) apparently was coined by U.S. social psychologist Leon Festinger, who developed the concept. Related: Cognitively.

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cognate (adj.)

1640s, "allied by blood, connected or related by birth, of the same parentage, descended from a common ancestor," from Latin cognatus "of common descent" (source also of Spanish cognado, Italian cognato), from assimilated form of com "together" (see co-) + gnatus, past participle of gnasci, older form of nasci "to be born" (from PIE root *gene- "give birth, beget").

Of things, "related in origin, traceable to the same source," by 1640s; specifically of words, "coming from the same root or original word but showing differences due to subsequent separate phonetic development," by 1782; of languages, "from the same original language," by 1799. French, Spanish, and Italian are cognate languages (all essentially descended from Latin) but are not cognate with Latin. English cognate, Spanish cognado and Italian cognato are cognate words from Latin cognatus. English brother, Sanskrit bhrtr-, Greek phratr, Latin frater, Russian brat are cognate words from the PIE root *bhrater. Words that are cognates are more like cousins than siblings; they develop in different languages.

Related: Cognatic; cognation (late 14c. in English as "blood-relationship, kinship"); cognateness. As a noun, "one connected to another by ties of kinship," from 1754.

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cognomen (n.)

1754, "a distinguishing name;" 1809, "a surname;" from Latin, from assimilated form of com "with, together" (see com-) + (g)nomen "name" (from PIE root *no-men- "name"). The last of the three names by which a Roman citizen was known (Caius Julius Csar, Marcus Tullius Cicero).

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cogency (n.)

"power of producing belief, quality of being highly probable or convincing," 1680s, from cogent + abstract noun suffix -cy.

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cogitative (adj.)

late 15c., "having the power of thinking or meditating," from Old French cogitatif (14c.), from Medieval Latin cogitativus, from Latin cogitare "to think" (see cogitation). Meaning "thoughtful, given to contemplation" is from 1650s.

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cognisant (adj.)
alternative spelling of cognizant (q.v.); also see -ize.
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cogitation (n.)

c. 1200, cogitacioun, "thought, idea, notion, that which is thought out; act of thinking, earnest reflection," from Old French cogitacion "thought, consideration, reflection," from Latin cogitationem (nominative cogitatio), noun of action from past participle stem of cogitare "to think, reflect, consider, turn over in the mind," which is apparently a contraction of co-agitare, from assimilated form of com "together" (see co-) + agitare, here in a sense of "to turn over in the mind," literally "to put in constant motion, drive, impel," frequentative of agere "to move, drive" (from PIE root *ag- "to drive, draw out or forth, move").

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cognisance (n.)
alternative spelling of cognizance (q.v.); also see -ize.
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