Definition from Wiktionary, the free dictionary
- Unthinking, not carefully considered, (nearly) automatic, spontaneous, easily predictable
- He gave a knee-jerk response.
reacting unthinkingly or spontaneously in an expected manner
knee-jerk (plural knee-jerks)
- A sudden reflexive movement of the leg below the knee, as a reaction to a tap to the tendon just below the patella (kneecap).
reflex extension of the lower leg due to tap below knee