The word 迅速 is formed by combining two independent characters, 迅 and 速, which both fundamentally mean "fast" or "quick". This is a classic example of a synonymous compound in Chinese, where two elements with very similar meanings are paired together to create a single, reinforced concept. The combination does not create a new, metaphorical meaning but instead intensifies and solidifies the core idea of swiftness, resulting in a word that conveys a strong, unambiguous sense of rapid speed or immediacy.