What does "knee-jerk" mean?

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

What is a synonym for "knee-jerk"?

Common synonyms include: kneejerk reflex, patellar reflex.

adj, noun

adj, noun ·Rare ·Advanced level

Noun

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).

Adjective

1
Unthinking, not carefully considered, (nearly) automatic, spontaneous, easily predictable.
"He gave a knee-jerk response."

"His knee-jerk reaction was to raise his voice at his child."

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

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.