Definitions of critical:

• adjective:   of or involving or characteristic of critics or criticism

  Example: "Critical acclaim"

• adjective:   marked by a tendency to find and call attention to errors and flaws

  Example: "A critical attitude"

• adjective:   characterized by careful evaluation and judgment

  Example: "A critical reading"

• adjective:   being in or verging on a state of crisis or emergency

  Example: "A critical shortage of food"

• adjective:   at or of a point at which a property or phenomenon suffers an abrupt change especially having enough mass to sustain a chain reaction

  Example: "A critical temperature of water is 100 degrees C--its boiling point at standard atmospheric pressure"

• adjective:   forming or having the nature of a turning point or crisis

  Example: "A critical point in the campaign"

• adjective:   urgently needed; absolutely necessary

  Example: "A critical element of the plan"