To hear clearly, you need more than one (3)
I believe the answer is:
ear
'one' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'to hear clearly you need more than' is the wordplay.
'EAR' is hidden within the letters.
However, I'm not sure how the hidden word is indicated.
Can you help me to learn more?
(Other definitions for ear that I've seen before include "Seed container" , "Part of corn plant" , "Auditory organ" , "Attention; seed head" , "Shell-like (slang)" .)