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

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

(weightlifting) The act of lifting the barbell from the floor to a resting position across the front of the shoulders (the clean phase), pausing, and thrusting the barbell over the head to a stationary position in one movement (the jerk phase). The normal technique for both parts of this act involves propelling the barbell upwards, quickly lowering the torso, and then straightening the legs.

present participle of jerk off

(vulgar) An act of masturbation.

(US, idiomatic, dated) A person who works at a soda fountain.

plural of jerk-off

Alternative spelling of jerkoff

plural of knee-jerk

(rail transport, derogatory) A branch line train, using light equipment