Sound young fellow, I see (5)

I believe the answer is:

sonic

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'sound' is the definition.
Both the answer and definition are adjectives. Maybe there's a link between them I don't understand?

'young fellow i see' is the wordplay.
'young fellow' becomes 'son' (I've seen this in another clue).
'see' becomes 'C' (the word for the letter, according to Chambers).
'son'+'i'+'c'='SONIC'

Can you help me to learn more?

(Other definitions for sonic that I've seen before include "Producing sound" , "Employing sound" , "Travelling at Mach One" , "Relating to sound waves" , "of noise" .)

I've seen this clue in the Evening Standard.

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