Here's the breakdown:
* Metaphor: A direct comparison between two unlike things without using "like" or "as." (e.g., "Life is a journey.")
* Metonymy: A figure of speech where something is referred to by something closely associated with it. (e.g., "The Crown" referring to the British monarchy.)
In "lend me your ear," we are not actually requesting someone's physical ear. We are asking them to pay attention to what we have to say, and the ear is associated with listening. Therefore, the phrase is a metonymy, not a metaphor.
Even though it's not a metaphor, it is still a figurative expression, meaning it uses words in a non-literal way to create an image or effect.