Etymology
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I.Q. 

1922, abbreviation of intelligence quotient, a 1921 translation of German Intelligenz-quotient, coined 1912 by German psychologist William L. Stern.

Intelligence is a general capacity of an individual consciously to adjust his thinking to new requirements: it is general mental adaptability to new problems and conditions of life. [Stern, "The Psychological Methods of Testing Intelligence," 1914]

Earlier, i.q. was an abbreviation of Latin idem quod "the same as."

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intelligence (n.)
Origin and meaning of intelligence
late 14c., "the highest faculty of the mind, capacity for comprehending general truths;" c. 1400, "faculty of understanding, comprehension," from Old French intelligence (12c.) and directly from Latin intelligentia, intellegentia "understanding, knowledge, power of discerning; art, skill, taste," from intelligentem (nominative intelligens) "discerning, appreciative," present participle of intelligere "to understand, comprehend, come to know," from assimilated form of inter "between" (see inter-) + legere "choose, pick out, read," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')."

Meaning "superior understanding, sagacity, quality of being intelligent" is from early 15c. Sense of "information received or imparted, news" first recorded mid-15c., especially "secret information from spies" (1580s). Meaning "a being endowed with understanding or intelligence" is late 14c. Intelligence quotient first recorded 1921 (see I.Q.).
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bozo (n.)
c. 1924, "muscular low-I.Q. male," perhaps from Spanish bozal, used in the slave trade and also to mean "one who speaks Spanish poorly." Bozo the clown was created 1940 at Capitol Records as the voice in a series of story-telling records for children ["Wall Street Journal," Oct. 31, 1983].
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