The meaning of the given phrase is that "an old friend always tell you the truth".
What are Idioms?
Idioms are phrases/sentences which are used to imply a certain meaning but the literary meaning of the word may differ from the implied meaning.
Explanation:
The phrase "The best mirror in the world is an old friend" is an idiom which means that our old friends are the person always tell us the truth even if it is harsh. They are the ones who actually care about us and tell us the correct path even if it is difficult to walk on that road. They act as a mirror to our true selves.
Therefore, the correct meaning is "an old friend always tell you the truth".
Learn more about Idioms on https://brainly.com/question/902417
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