C: a commonly used metaphor that has become part of ordinary language.
Explanation:
A metaphor is a <em>figure of speech</em> that compares two things by saying that one thing is another. A dead metaphor are those metaphors that, traditionally, have lost their force, but continue as <em>clichés</em>, or <em>everyday idioms</em>. For example: The <em>face</em> or <em>hand</em> of a watch no longer bring the comparison with parts of the human body.
