Etymology
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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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counterintelligence (n.)

also counter-intelligence, "act of preventing an enemy from obtaining secret information," 1940, from counter- + intelligence.

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intelligentsia (n.)
"the intellectual class collectively," 1905, from Russian intelligyentsiya, from Latin intelligentia "intelligence" (see intelligence). Perhaps via Italian intelligenzia.
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intelligencer (n.)
1580s, "spy, informant," agent noun from intelligence. Perhaps modeled on French intelligencier or Italian intelligentiere. Meaning "bringer of news, one who conveys intelligence" is from 1630s; as a newspaper name from 1640s.
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AI 
also a.i., by 1971, abbreviation of artificial intelligence. In early 20c. it stood for artificial insemination.
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intelligent (adj.)
c. 1500, a back-formation from intelligence or else from Latin intelligentem (nominative intelligens), present participle of intelligere. Intelligent design, as a name for an alternative to atheistic cosmology and the theory of evolution, is from 1999. Related: Intelligently.
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intellection (n.)
c. 1400, intellecioun "meaning, purpose;" mid-15c., "the understanding;" 1610s, "an act of understanding," from Old French intelleccion and directly from Medieval Latin intellectionem (nominative intellectio), noun of action from past participle stem of Latin intelligere "to understand, discern" (see intelligence).
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intellect (n.)
"the sum of the cognitive facilities (except sense or sense and imagination), the capacity for reasoning truth," late 14c. (but little used before 16c.), from Old French intellect "intellectual capacity" (13c.), and directly from Latin intellectus "discernment, a perception, understanding," noun use of past participle of intelligere "to understand, discern" (see intelligence). The Latin word was used to translate Greek nous "mind, thought, intellect" in Aristotle.
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intelligible (adj.)
late 14c., "able to understand, intelligent," from Latin intelligibilis, intellegibilis "that can understand; that can be understood," from intellegere "to understand, come to know" (see intelligence). In Middle English also "to be grasped by the intellect" (rather than the senses). In English, sense of "capable of being understood, that can be understood" first recorded c. 1600. Related: Intelligibly.
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intellectual (adj.)
late 14c., "grasped by the understanding" (rather than by the senses), from Old French intellectuel (13c.) and directly from Latin intellectualis "relating to the understanding," from intellectus "discernment, understanding," noun use of past participle of intelligere "to understand, discern" (see intelligence).

Sense of "characterized by a high degree of intellect" is from 1819. Meaning "appealing to or engaging the mental powers" is from 1834. Intellectual property "products of the intellect" is attested from 1845. Adjective formations in the sense "of or pertaining to the intellect" included intellective (early 15c.), intellectile (1670s).
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