reflex

1 of 2

noun

re·​flex ˈrē-ˌfleks 

1

a

archaic : reflected heat, light, or color

b

: a mirrored image

c

: a copy exact in essential or peculiar features

2

a

: an automatic and often inborn response to a stimulus that typically involves a nerve impulse passing inward from a receptor to the spinal cord and then passing outward from the spinal cord to an effector (such as a muscle or gland) without reaching the level of consciousness and often without passing to the brain

the knee-jerk reflex

b

: the process that culminates in a reflex and comprises reception, transmission, and reaction

called also reflex action

c

reflexes plural : the power of acting or responding with adequate speed

d

: a way of thinking or behaving

3

: a linguistic element (such as a word or sound) or system (such as writing) that is derived from a prior and especially an older element or system

boat is the reflex of Old English bāt

reflex

2 of 2

adjective

1

: directed back on the mind or its operations : introspective

2

: reflexed

3

: produced or carried out in reaction, resistance, or return

4

of an angle : being between 180° and 360°

5

: of, relating to, or produced by a reflex without intervention of consciousness

reflexly adverb

Examples of reflex in a Sentence

Noun

reflexes such as swallowing and blinking

Disagreeing with my suggestions has become almost a reflex for him.

an athlete with great reflexes

My reflexes are slower now that I'm older.

Recent Examples on the Web

Noun

These improvements to system zero reflexes are described by executives as an essential safety feature, given that a falling robot could cause injury or property damage, or even a fire. —Billy Perrigo, Time, 9 Oct. 2025

Oracle shares, down more than 5% in the initial reflex, narrowed the losses by day’s end but remained under pressure. —Michael Santoli, CNBC, 7 Oct. 2025

Adjective

In each case, there's a recognition that some players might want to explore a game's world—to experience the characters, art, and dialogue that the developers worked so hard to craft—without struggling through mechanical reflex tests or grindy, repetitive challenges. —ArsTechnica, 9 Oct. 2025

This realistic doctor’s coat has everything your aspiring doctor needs to give their patients a check-up, including a face mask, a stethoscope with sound effects (AAA batteries not included), thermometer, syringe, reflex hammer, and reusable name tag. —Katrina Cossey, Parents, 1 Oct. 2025

Word History

Etymology

Noun

Latin reflexus, past participle of reflectere to reflect

Adjective

Latin reflexus

First Known Use

Noun

1508, in the meaning defined at sense 1a

Adjective

1607, in the meaning defined at sense 1

Phrases Containing reflex

• Babinski reflex
• Babinski's reflex
• reflex arc
• reflex sympathetic dystrophy
• single-lens reflex

Kids Definition

reflex

1 of 2 noun

re·​flex ˈrē-ˌfleks 

1

: an automatic response to a stimulus in which a nerve message passes from a sense organ to the spinal cord and then to a point of action (as a muscle or gland) often without first passing to the brain

the knee-jerk reflex

compare habit sense 3

2

plural : the power of acting or responding with enough speed

an athlete with great reflexes

reflex

2 of 2 adjective

1

: produced in reaction, resistance, or return

2

: of, relating to, or produced by a reflex of the nervous system

reflex action

reflexly adverb

Medical Definition

reflex

1 of 2 noun

re·​flex ˈrē-ˌfleks 

1

a

: reflected heat, light, or color

b

: a mirrored image

2

a

: an automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to the spinal cord and thence outward to an effector (as a muscle or gland) without reaching the level of consciousness and often without passing to the brain

the knee-jerk reflex

b

: the process that culminates in a reflex and comprises reception, transmission, and reaction

c

reflexes plural : the power of acting or responding with adequate speed

reflex

2 of 2 adjective

1

: bent, turned, or directed back : reflected

2

: of, relating to, or produced by a reflex without intervention of consciousness