CRUCIAL, having the form of a cross, as the "crucial liga ments" of the knee-joint, which cross each other, connecting the femur and the tibia (Lat. crux, a cross) ; from Francis Bacon's expression instantia crucis (from the finger-post or crux at cross roads), decisive, finally choosing between two alternatives, hence, generally, a synonym for "critical." The word is also used, with a reference to the use of a "crucible," of something which tests and tries.