knee jerk

¹

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

[nee-jurk]

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

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

Word History and Origins

Origin of knee jerk¹

First recorded in 1875–80

Origin of knee jerk²

First recorded in 1895–1900