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."

updated on November 30, 2017

Definitions of I.Q. from WordNet

I.Q. (n.)
a measure of a person's intelligence as indicated by an intelligence test; the ratio of a person's mental age to their chronological age (multiplied by 100);
Synonyms: intelligence quotient / iq
Etymologies are not definitions. From, not affiliated with etymonline.