Crossword Genius

Second hearing (4)

Ross

I believe the answer is:

echo

I'm a little stuck... Click here to teach me more about this clue!

This clue might be a double definition.

'second' is the first definition.
(I've seen this in another clue)

'hearing' is the second definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

Can you help me to learn more?

(Other definitions for echo that I've seen before include "Repeat or reverberate" , "Rebounding sound" , "Ape" , "Greek girl in love with Narcissus" , "A natural sound reflection" .)

I've seen this clue in The Telegraph.
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