from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Easily predictable; automatic.
  • adjective Reacting spontaneously in the expected manner.

from The Century Dictionary.

  • noun A sudden jerking of the knee, caused by a contraction of the quadriceps femoris, evoked by a blow on the patellar tendon or in any way that gives the quadriceps a sudden tug. Also called patellar tendon reflex and knee-kick.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective Automatic, spontaneous, easily predictable
  • noun A sudden reflexive movement of the leg below the knee, as a reaction to a tap to the tendon just below the patella (kneecap).


from Wiktionary, Creative Commons Attribution/Share-Alike License

knee +‎ jerk, First attested 1876, obviously derived from a figurative sense of the patellar reflex.



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