1. If a project or organization goes critical, it reaches a stage of development where it can operate smoothly and successfully. The programme confirmed its initial impact in week two, and really `went critical' with the third edition on 8 December. Bristol airport is about to go critical. That will come when more than a million passengers a year pass through the terminal.

2. When a nuclear power station goes critical, it reaches a state in which a nuclear fission chain reaction can sustain itself. Monju went critical last year, and produced its first electricity in August this year.