subcritical Syllabification: (sub·crit·i·cal)Pronunciation: /səbˈkritikəl/Definition of subcritical adjective Physics below a critical threshold, in particular. (in nuclear physics) containing or involving less than the critical mass. (of a flow of fluid) slower than the speed at which waves travel in the fluid. subcritical in other Oxford dictionaries Definition of subcritical in the British & World English dictionary