The word 借口 is formed through a vivid conceptual blend: 借 means "to borrow" or "to use", and 口 means "mouth" or "speech". Together, they create the metaphorical image of "borrowing words from one's mouth", that is, taking readily available speech or a pre-existing line of reasoning, to fashion a constructed justification or pretext for an action. It conveys the idea of opportunistically assembling spoken words into a facade of a reason, much like borrowing materials to build a temporary cover.