The Collaborative International Dictionary of English v.0.48:

IQ \IQ\, IQ \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).

   Syn: intelligence quotient, IQ.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

I.Q.
    n 1: 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) [syn:
         intelligence quotient, IQ, I.Q.]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "IQ":
   Bernreuter personality inventory, Binet-Simon test,
   Brown personality inventory, Goldstein-Sheerer test, IQ test,
   Kent mental test, Minnesota preschool scale, Oseretsky test,
   Rorschach test, Stanford revision, Stanford-Binet test,
   Szondi test, TAT, Wechsler-Bellevue intelligence scale,
   achievement test, alpha test, apperception test, apprehension,
   aptitude test, association test, beta test, caliber, capacity,
   comprehension, conception, controlled association test,
   deductive power, esemplastic power, free association test,
   ideation, inkblot test, integrative power, intellect,
   intellectual grasp, intellectual power, intellectualism,
   intellectuality, intelligence, intelligence quotient,
   intelligence test, interest inventory, knowledge, mental age,
   mental capacity, mental grasp, mental ratio, mental test,
   mentality, mother wit, native wit, personality test, power of mind,
   psychological test, rationality, reasoning power, sanity,
   scope of mind, sense, standardized test,
   thematic apperception test, thinking power, understanding, wit,
   word association test