The word 急救 is formed by combining two independent characters, each contributing a core concept to create a new, unified meaning. The first character, 急 (jí), conveys the idea of urgency, haste, or an emergency situation. It is directly joined with the second character, 救 (jiù), which carries the meaning of to rescue, to save, or to provide aid. When placed together, the combination logically and intuitively represents "urgent rescue" or "emergency aid", specifically referring to immediate medical assistance, hence, "first aid". The formation is a direct conceptual fusion of the circumstance (急) and the required action (救).