Definition of "critical"

critical

/ˈkɹɪt.ɪ.kəl/

adjective
comparative more critical, superlative most critical
1. Inclined to find fault or criticize.
2. Pertaining to, or indicating, a crisis or turning point.
  Quotations
  Such a scandal as the prosecution of a brother for forgery—with a verdict of guilty—is a most truly horrible, deplorable, fatal thing. It takes the respectability out of a family perhaps at a critical moment, when the family is just assuming the robes of respectability: […] it is a black spot which all the soaps ever advertised could never wash off.
  1892, Walter Besant, “Prologue: Who is Edmund Gray?”, in The Ivory Gate […], New York, N.Y.: Harper & Brothers, […]
3. Extremely important.
  Quotations
  Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis: […] . The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light. The critical component of the photosynthetic system is the “water-oxidizing complex”, made up of manganese atoms and a calcium atom.
  2013 September-October, Katie L. Burke, “In the News”, in American Scientist
  Third Pole glaciers are critical to billions of people from Vietnam to Afghanistan.
  2018, VOA Learning English > China's Melting Glacier Brings Visitors, Adds to Climate Concerns‎
4. Relating to criticism or careful analysis, such as literary or film criticism.
  Quotations
  “Unless you are purchasing cereal from a health food store, many brands that are marketed as healthy are usually full of sugar and processed ingredients,” says Garcia. So when you’re choosing cereal, bread or any other whole-grain product, Garcia recommends reading labels with a critical eye.
  2012 April 19, Alexandra Sifferlin, “‘Healthy’ Foods that Really Aren’t: Nutritionists Weigh In”, in Time‎
5. (medicine) Of a patient condition involving unstable vital signs and a prognosis that predicts the condition could worsen; or, a patient condition that requires urgent treatment in an intensive care or critical care medical facility.
6. (medicine, by extension) In such a condition.
7. Likely to go out of control if disturbed, that is, opposite of stable.
8. (physics) Of the point (in temperature, reagent concentration etc.) where a nuclear or chemical reaction becomes self-sustaining.
9. (physics) Of a temperature that is equal to the temperature of the critical point of a substance, i.e. the temperature above which the substance cannot be liquefied.
noun
plural criticals
1. A critical value, factor, etc.
  Quotations
  The second undamped system criticals show a greater percentage depression than the first.
  1976, American Society of Mechanical Engineers, Journal of engineering for industry, volume 98, page 508
  Finally, criticals are high-risk, high-value items that give the final product a competitive advantage in the marketplace […] Criticals, in part, determine the customer's ultimate cost of using the finished product — in our example, the computer.
  2008, John J. Coyle, C. John Langley, Brian Gibson, Supply Chain Management: A Logistics Perspective, page 564
2. In breakdancing, a kind of airflare move in which the dancer hops from one hand to the other.