The Chinese idiom "千钧一发" is formed by sequentially combining the character for "thousand" (千), the ancient unit of weight "jun" (钧), meaning approximately 30 catties, the character for "one" (一), and the character for "hair" (发), literally translating to "a thousand jun hanging by a single hair". This construction directly juxtaposes an immense weight with a fragile thread to depict a scenario of extreme peril.