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knee-jerk reflex

Cultural  
  1. A sudden involuntary forward movement of the lower leg that can be produced by a firm tap to the tendon located just below the kneecap.


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The term is loosely applied to any response or belief that is automatic rather than thoughtful. In this sense, it is usually a term of reproach: “Smith is a knee-jerk liberal.”

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

My self-deprecating remarks, a knee-jerk reflex with me, didn’t amuse him.

From Los Angeles Times • Jan. 12, 2023

“It’s like they go into hibernation from the overwhelming stress. Their brain switches off engagement with their social environment. They don’t respond to pain. Their knee-jerk reflex is absent.”

From Washington Times • Sep. 3, 2018

“It’s like they go into hibernation from the overwhelming stress. Their brain switches off engagement with their social environment. They don’t respond to pain. Their knee-jerk reflex is absent.”

From Seattle Times • Sep. 2, 2018

They see it as not just a knee-jerk reflex but as something we can control.

From New York Times • Mar. 21, 2016

For the leg, the knee-jerk reflex of the quadriceps is common, as is the ankle reflex for the gastrocnemius and soleus.

From Textbooks • Jun. 19, 2013

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