Inclined to judge severely and find fault. Characterized by careful, exact evaluation and judgment: a critical reading. Of, relating to, or characteristic of critics or criticism: critical acclaim; a critical analysis of Melville's writings. Forming or having the nature of a turning point; crucial or decisive: a critical point in the campaign. Of or relating to a medical crisis: an illness at the critical stage. Being or relating to a grave physical condition especially of a patient. Indispensable; essential: a critical element of the plan; a second income that is critical to the family's well-being. Being in or verging on a state of crisis or emergency: a critical shortage of food. Fraught with danger or risk; perilous. Mathematics Of or relating to a point at which a curve has a horizontal tangent line, as at a maximum or minimum. Chemistry & Physics Of or relating to the value of a measurement, such as temperature, at which an abrupt change in a quality, property, or state occurs: A critical temperature of water is 100\u00b0C, its boiling point at standard atmospheric pressure. Physics Capable of sustaining a nuclear chain reaction.