Jump To:

• 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.

---

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.

---

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

---

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

“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

In the past, Campbell said, India’s leaders have had “almost a knee jerk reaction” to resist such massive multilateral projects.

From Seattle Times ● Sep. 8, 2023

Anxious attention to the knee jerk inhibits it; gritting the teeth or clenching the fist reinforces it.

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

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

Trouble is, given a sudden, sharp jump in valuations, any adjustment will need to be made over time, not in a knee-jerk way.

From The Wall Street Journal ● Apr. 7, 2026

Typically, the knee-jerk response to all of this is, “So what? Just don’t commit crimes and you have nothing to worry about.”

From Salon ● Feb. 20, 2026

It’s a knee-jerk reaction, so fast I forget for a second that I’m furious at him.

From "Legendary Frybread Drive-In" by Cynthia Leitich Smith