In its simplest sense, a metaphor is a figure of speech where, essentially, a simile is ellipted to what is apparently a false statement, but as the intention is to emphasise the similarity rather than deceive, this is an accepted linguistic device.
Bob is like a tiger.
Bob is a tiger.
John Lawler is an expert on pointing out in his invaluable and fascinating contributions the extended metaphors on which a lot of our language is built, such as the container metaphor(s) and up-is-achievement metaphor. In a recent post, he pointed out that 'zenith' is used metaphorically as 'high point [of eg a career]'.
However, Wikipedia has this to say about dead metaphors:
There is debate among literary scholars whether so-called "dead metaphors" are dead or are metaphors. Literary scholar R.W. Gibbs noted that for a metaphor to be dead, it would necessarily lose the metaphorical qualities that it comprises. These qualities, however, still remain. A person can understand the expression "falling head-over-heels in love" even if they have never encountered that variant of the phrase "falling in love."
Analytic philosopher Max Black argued that the dead metaphor should not be considered a metaphor at all, but rather classified as a separate vocabulary item. If the verb "to plough" retained the simple meaning of "to turn up the earth with a plough," then the idea of a car "ploughing through traffic" would clearly be a metaphor. The expression would be a comparison between the motion of the plough cutting through the soil and a car speeding through traffic. In order to understand it, one would need to grasp the comparison. However, "to plough" has taken on an additional meaning of "to move in a fast and uncontrolled manner," and so to say that a car "ploughed through the traffic" is a literal statement. No knowledge of the original metaphorical symbolism is necessary to understanding the statement.
For 'zenith', Elliott Frith found a dictionary definition:
the strongest or most successful period of time
Should we revise our usage of the word 'metaphor' in such cases?