The word 贸易 is formed by combining two characters, 贸 (mào) and 易 (yì), which together create a compound word. Each character contributes a related meaning: 贸 originally conveyed the idea of exchanging or bartering goods, while 易 means to exchange or change. Their combination reinforces and specifies the concept of a mutual, commercial exchange, evolving to represent the modern meaning of "trade" or "commerce" as a single, unified concept.