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• knee jerk
  knee jerk

  noun

  a reflex extension of the leg, caused by contraction of the quadriceps, resulting from a sharp tap on the patellar tendon; patellar reflex.
• knee-jerk
  knee-jerk

  adjective

  of or relating to a knee-jerk.

knee jerk

¹ American  

noun

1. a reflex extension of the leg, caused by contraction of the quadriceps, resulting from a sharp tap on the patellar tendon; patellar reflex.

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knee-jerk ² American  

[nee-jurk] / ˈniˌdʒɜrk /

adjective

1. of or relating to a knee-jerk.

2. Informal. reacting according to a certain habitual manner; unthinking.

   a knee-jerk liberal.

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knee jerk British  

noun

1. Also called: patellar reflex. physiol an outward reflex kick of the lower leg caused by a sharp tap on the quadriceps tendon just below the patella

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1. made or occurring as a predictable and automatic response, without thought

   kneejerk support

Etymology

Origin of knee jerk¹

First recorded in 1875–80

Origin of knee-jerk²

First recorded in 1895–1900

Example Sentences

See Examples For:

knee jerk knee-jerk

When asked about how tough sentencing in Northern Ireland is Dame Siobhan said there can be a "knee jerk reaction".

From BBC ● Sep. 7, 2026

“The knee jerk is likely disappointment, given the lack of acceleration in both billed business and revenue growth,” Foran said.

From The Wall Street Journal ● Jul. 24, 2026

“Investors do not want to see this and the negative knee jerk reaction is being seen,” Ives said of Alphabet stock’s drop.

From Barron's ● Jun. 22, 2026

"Everyone recognizes there is a growing antibiotic resistance crisis, and the knee jerk reaction is to develop new antibiotics," You added.

From Science Daily ● Feb. 22, 2024

We see excellent examples of cerebral facilitation and inhibition in the case of the knee jerk.

From Psychology A Study Of Mental Life by Robert S. Woodworth

Brychan reassured teachers and leaders that there would be no knee-jerk response to the results and plans were in place to support schools to raise standards.

From BBC ● Sep. 8, 2026

The currency could suffer knee-jerk weakness if the Fed holds rates steady, TD Securities said.

From The Wall Street Journal ● Jul. 29, 2026

A knee-jerk reaction to an underwhelming report could trigger a substantial slide.

From Barron's ● Jun. 24, 2026

My immediate knee-jerk reaction to your portfolio is that you have nearly 39% of your total holdings in stocks, which is OK.

From MarketWatch ● Apr. 22, 2026

They didn’t just have a knee-jerk reaction to immediately respond to the text.

From "A Deadly Wandering: A Mystery, a Landmark Investigation, and the Astonishing Science of Attention in the Digital Age" by Matt Richtel