• synonyms


[adjective, noun ree-fleks; verb ri-fleks]
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  1. Physiology. noting or pertaining to an involuntary response to a stimulus, the nerve impulse from a receptor being transmitted inward to a nerve center that in turn transmits it outward to an effector.
  2. occurring in reaction; responsive.
  3. cast back; reflected, as light, color, etc.
  4. bent or turned back.
  5. designating a radio apparatus in which the same circuit or part performs two functions.
  1. Physiology.
    1. Also called reflex act.movement caused by a reflex response.
    2. Also called reflex action.the entire physiological process activating such movement.
  2. any automatic, unthinking, often habitual behavior or response.
  3. the reflection or image of an object, as exhibited by a mirror or the like.
  4. a reproduction, as if in a mirror.
  5. a copy; adaptation.
  6. reflected light, color, etc.
  7. Historical Linguistics. an element in a language, as a sound, that has developed from a corresponding element in an earlier form of the language: The (ō) in “stone” is a reflex of Old English ā.
  8. a reflex radio receiver.
  9. a reflex camera.
verb (used with object)
  1. to subject to a reflex process.
  2. to bend, turn, or fold back.
  3. to arrange in a reflex system.

Origin of reflex

1500–10; < Latin reflexus bent back, past participle of reflectere to reflect
Related formsre·flex·ly, adverbre·flex·ness, nounmul·ti·re·flex, nounsem·i·re·flex, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for reflex-action

Historical Examples

  • Even the psychologist with his reflex-action theory does not solve the whole problem.

    The Book of Khalid

    Ameen Rihani

British Dictionary definitions for reflex-action


noun (ˈriːflɛks)
    1. an immediate involuntary response, esp one that is innate, such as coughing or removal of the hand from a hot surface, evoked by a given stimulus
    2. (as modifier)a reflex action See also reflex arc
    1. a mechanical response to a particular situation, involving no conscious decision
    2. (as modifier)a reflex response
  1. a reflection; an image produced by or as if by reflection
  2. a speech element derived from a corresponding form in an earlier state of the language"sorrow" is a reflex of Middle English "sorwe"
adjective (ˈriːflɛks)
  1. maths (of an angle) between 180° and 360°
  2. (prenominal) turned, reflected, or bent backwards
verb (rɪˈflɛks)
  1. (tr) to bend, turn, or reflect backwards
Derived Formsreflexible, adjectivereflexibility, noun

Word Origin

C16: from Latin reflexus bent back, from reflectere to reflect
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for reflex-action



c.1500, "reflection of light," from verb reflex meaning "refract, deflect" (late 14c.), from Late Latin reflexus "a bending back," noun use of past participle of reflectere (see reflection). Meaning "involuntary nerve stimulation" first recorded 1877, from reflex action (1833).

Online Etymology Dictionary, © 2010 Douglas Harper

reflex-action in Medicine

abdominal reflexes

  1. Contractions of the muscles of the abdominal wall upon stimulation of the skin or upon the tapping of neighboring bony structures.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

reflex-action in Science


  1. An involuntary physiological response to a stimulus, as the withdrawal of a body part from burning heat.
  2. An unlearned or instinctive response to a stimulus. Also called unconditioned response See more at classical conditioning.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

reflex-action in Culture

knee-jerk reflex

A sudden involuntary forward movement of the lower leg that can be produced by a firm tap to the tendon located just below the kneecap.


The term is loosely applied to any response or belief that is automatic rather than thoughtful. In this sense, it is usually a term of reproach: “Smith is a knee-jerk liberal.”
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.