1. inclined to find fault or to judge with severity, often too readily.
2. occupied with or skilled in criticism.
3. involving skillful judgment as to truth, merit, etc.; judicial: a critical analysis.
4. of or pertaining to critics or criticism: critical essays.
5. providing textual variants, proposed emendations, etc.: a critical edition of Chaucer.
6. pertaining to or of the nature of a crisis: a critical shortage of food.
7. of decisive importance with respect to the outcome; crucial: a critical moment.
8. of essential importance; indispensable: a critical ingredient.
9. Medicine/Medical. Having unstable and abnormal vital signs and other unfavorable indicators.
a. pertaining to a state, value, or quantity at which one or more properties of a substance or system undergo a change.
b. (of fissionable material) having enough mass to sustain a chain reaction.