(a)criticalat or of a point at which a property or phenomenon suffers an abrupt change especially having enough mass to sustain a chain reaction“a critical temperature of water is 100 degrees C--its boiling point at standard atmospheric pressure”, “critical mass”, “go critical”
(a)criticalbeing in or verging on a state of crisis or emergency“a critical shortage of food”, “a critical illness”, “an illness at the critical stage”
(s)critical, vitalurgently needed; absolutely necessary“a critical element of the plan”, “critical medical supplies”, “vital for a healthy society”, “of vital interest”