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knee-jerk reflex

n.
  1. patellar reflex

knee-jerk reflex in Culture

knee-jerk reflex

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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Note

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.”
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.