The word "信用卡" is formed by conceptually combining three ideas into a single, logical unit: it starts with "信" (xìn), meaning trust or credit, which is the foundational principle. This trust is specifically applied to "用" (yòng), meaning to use or spend, indicating the actionable function. Finally, this function of spending based on credit is materialized in the form of a "卡" (kǎ), a card. Thus, the term sequentially builds from the abstract concept (credit) to its purpose (spending) to its physical form (card), creating the complete concept for a "credit card".