The junior, I see, is sound (5)
I believe the answer is:
sonic
'sound' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I can't see?
'the junior i see' is the wordplay.
'the junior' becomes 'son' (I've seen this in another clue).
'see' becomes 'C' (the word for the letter, according to Chambers).
'son'+'i'+'c'='SONIC'
'is' is the link.
Can you help me to learn more?
(Other definitions for sonic that I've seen before include "of noise" , "Involving sound waves, say a boom" , "Sort of boom" , "Type of boom" , "Boom of jet aircraft" .)