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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

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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

Cross the knee to be stimulated over the other leg, and tap the tendon just below the knee cap, and the knee jerk appears.

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

Since the faces on display are unusually eclectic, the knee-jerk reaction is to fear the movie is making fun of them.

From Los Angeles Times ● Oct. 23, 2026

But Piti said the BOT’s experience with shocks like wars and tariffs has taught it to avoid knee-jerk reactions.

From The Wall Street Journal ● Oct. 14, 2026

As if this knee-jerk response were anticipated, Sally reassures the audience that what they came to see will be different than what transpired before.

From Salon ● Sep. 14, 2026

A left-back is essential and this is not just a knee-jerk reaction to the defeat at Hull City - you can see United are short in that position.

From BBC ● Aug. 25, 2026

Part of it was the new, knee-jerk anger, but mostly he was thinking of Lily.

From "We'll Fly Away" by Bryan Bliss

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