subcritical

[suhb-krit-i-kuh l]
adjective
  1. Physics. pertaining to a state, value, or quantity that is less than critical, especially to a mass of radioactive material.
  2. being of less than critical importance.

Origin of subcritical

First recorded in 1940–45; sub- + critical
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for subcritical

subcritical

adjective
  1. physics (of a nuclear reaction, power station, etc) having or involving a chain reaction that is not self-sustaining; not yet critical
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012