reflex

reflex — noun

IPA/ˈriːfleks/
KK[rˈiflɛks]IPA/ˈriːfleks/
  • reflexsingular
  • reflexesplural

1. An automatic body response to something that happens, such as a tap just below t

1.nounB2
Definition

An automatic body response to something that happens, such as a tap just below the knee making the lower leg kick forward, which happens without conscious thought.

Example

During the check-up, Dr. Okafor tapped Noor's knee with a small hammer to test her reflex.

stimulus-response pattern: tap knee → leg kick

Pulling your hand from a hot stove is an automatic reflex that protects you from burns.

Common collocations
  • knee-jerk reflex
  • gag reflex
  • pupil reflex
  • conditioned reflex
  • reflex to light
Synonyms
  • instinct

    broader — instinct covers complex behaviors (nest-building, migration), while reflex refers only to simple physical responses

  • involuntary response

    more formal and descriptive; less common in everyday speech

Antonyms
  • voluntary action

    an action you decide to do on purpose, the opposite of an automatic reflex

Grammar Patterns

reflex + to + stimulus

possessive + reflex

Usage Note

Commonly followed by the preposition 'to' to name the stimulus — for example, a reflex to light or a reflex to sound. Also appears in compound terms naming specific body reflexes, such as knee-jerk reflex, pupil reflex, and gag reflex.

Common Mistakes

He blinked by reflex after deciding to.
He blinked by reflex when the flashlight hit his eyes.
A reflex is automatic and not controlled by conscious decision.

2. The natural speed with which a person responds physically or mentally to somethi

2.nounB1
Definition

The natural speed with which a person responds physically or mentally to something sudden or unexpected — for example, catching a falling object or swerving to avoid a car.

Example

Ravindra's quick reflexes helped him catch the falling glass before it hit the kitchen floor.

collocation: quick reflexes

Top tennis players need excellent reflexes to return serves that travel very fast.

collocation: excellent reflexes

Common collocations
  • quick reflexes
  • good reflexes
  • lightning reflexes
  • sharp reflexes
  • reflexes + slow down
Synonyms
  • reaction time

    more specific — measures the exact time interval; reflexes is broader and more natural in everyday speech

  • quickness

    general term for speed; less specific to responding to events

Grammar Patterns

possessive + reflexes

good/quick/lightning + reflexes

Usage Note

Almost always appears in the plural form 'reflexes' when referring to a person's general ability to react quickly. The singular 'reflex' in this sense is rare and usually occurs in set phrases like 'a lightning reflex'.

Common Mistakes

He has good reflex.
He has good reflexes.
Use the plural form for the general ability to react quickly.

3. A modern word or sound that has developed from a specific word or sound in an ol

3.nounC1
Definition

A modern word or sound that has developed from a specific word or sound in an older form of the same language or a parent language.

Example

Yael pointed at the whiteboard, showing how Latin 'lac' became Spanish 'leche' over time.

pattern: reflex of [source language word]

Ryo flipped through an Old English dictionary to find the reflex of the modern word 'loaf'.

Common collocations
  • reflex of Latin
  • modern reflex
  • regular reflex
  • direct reflex
Synonyms
  • descendant

    more general term for anything that develops from an earlier form; less technical than reflex

  • derivative

    broader — can refer to words formed by adding affixes, not just historical development

Antonyms
  • ancestor

    the earlier word from which a reflex develops

Grammar Patterns

reflex + of + source language word

Usage Note

A technical term in historical linguistics. The source language is usually specified after the preposition 'of'. Contrast with 'cognate', which refers to related words in sister languages that share a common ancestor rather than one deriving from the other.

reflex — adjective

IPA/ˈriː.fleks/
KK[rˈiflɛks]IPA/ˈriː.fleks/

Word family

  • reflexive
    adjectiveB2
  • reflexively
    adverbC1
  • reflexivity
    nounC1

Synonym discussion

Sense: noun/2

Reflexes, reaction time, instinct, and quickness all relate to speed of response, but they differ in focus. Reflexes (almost always plural) refers to the general ability to act fast in unexpected situations, especially in sports or driving contexts — 'He has great reflexes.' Reaction time is more precise and scientific: it measures the exact interval between a stimulus and a response, often tested in psychology labs. Instinct describes an inborn pattern of behaviour rather than the speed of a single response — animals build nests by instinct, but they don't have 'quick instincts.' Quickness is a broader word that can describe speed in any kind of movement or thinking. In everyday conversation, 'reflexes' is the most natural choice when talking about catching, dodging, or reacting to fast-moving events.

reflexes ↗reaction timeinstinct ↗quickness

Common collocations

Nouns

Adverbs

Phrases

  • by reflex
  • a reflex to [stimulus]

Prepositions

Etymology

LatinEnglish

The word 'reflex' traces back to the Latin verb 'reflectere' — 're-' meaning 'back' and 'flectere' meaning 'to bend'. In the 1500s, English borrowed 'reflex' as a noun meaning 'reflected light' or 'a reflection'. The modern scientific sense of an involuntary body response developed in the early 1800s, when physiologists discovered that certain nerve signals 'bend back' toward the spinal cord without reaching the brain. The adjective use describing automatic actions followed soon after.