The quality, state, or degree of being of the highest importance: "The challenge of our future food supply is approaching criticality” ( New York Times).
Physics The point at which a nuclear reaction is self-sustaining.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.