knee-jerk

• kneejerk, knee jerk

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

knee-jerk (comparative more knee-jerk, superlative most knee-jerk)

1. Unthinking, not carefully considered, (nearly) automatic, spontaneous, easily predictable.

   He gave a knee-jerk response.

   • 2022 March 23, Nigel Harris, “Comment: Drains, trains and Control”, in RAIL, number 953, page 3:

     There were knee-jerk demands from trade unions for immediate withdrawal of all HSTs; these were wrong-headed.

   • 2023 March 15, Michael J. de la Merced, Maureen Farrell, “Credit Suisse to Borrow Up to $54 Billion From Central Bank”, in The New York Times‎:

     The knee-jerk reaction is further evidence of just how panicked investors are about the stability of the global financial system after the collapse of Silicon Valley Bank last week.

• knee-jerkish
• knee-jerkishly
• knee-jerky

knee-jerk (plural knee-jerks)

1. A sudden reflexive movement of the leg below the knee, as a reaction to a tap to the tendon just below the patella (kneecap).

• kneejerk reflex
• patellar reflex