The word "热线" is formed by directly combining two characters: "热" (rè), meaning "hot", and "线" (xiàn), meaning "line" or "wire". It is a conceptual metaphor where the quality of "hot" , implying urgency, immediacy, and high activity , is applied to a "line" of communication. This creates a new, integrated concept for a direct, prioritized telephone or communication channel, famously originating from the Cold War "hotline" for instant contact between world leaders to prevent crisis.