This is a metaphor that has lost its original meaning through extensive use. The term is used to demonstrate that the phrase no longer acts as a metaphor it has just become a plain phrase with a sim?

A metaphor that has lost its original impact due to overuse is often referred to as a "dead metaphor." Such phrases, like "the foot of the mountain" or "the heart of the matter," have become so commonplace that they no longer evoke vivid imagery or provoke thought, functioning instead as straightforward expressions. As a result, they lose their metaphorical power and can be seen as merely conventional language.