A dead metaphor is a metaphor that has been used so often that speakers no longer feel its original image. The phrase still carries its figurative history, but in ordinary use it functions like a familiar expression rather than a fresh comparison. Writers may still use dead metaphors, but their figurative force is usually faded.
Example
The deadline is approaching fast.
We need to get to the root of the problem.
She kept her feelings bottled up for years.
Related Definitions
[n] a metaphor that has occurred so often that it has become a new meaning of the expression (e.g., `he is a snake' may once have been a metaphor but after years of use it has died and become a new sense of the word `snake')