[{"Bold_text": "noun", "List Items": ["a reflex extension of the leg, caused by contraction of the quadriceps, resulting from a sharp tap on the patellar tendon; patellar reflex."]}, {"Bold_text": "adjective", "List Items": ["of or relating to a knee-jerk.", "Informal.reacting according to a certain habitual manner; unthinking:a knee-jerk liberal."]}]