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Chief relative going after first degree (3,6)

Ross

I believe the answer is:

top banana

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

'chief relative going after' is the wordplay.
'chief' becomes 'top' ('top' can be a synonym of 'chief').
'relative going' becomes 'banana' (I can't explain this - if you can you should give a lot more credence to this answer).
'after' says to put letters next to each other.
'top'+'banana'='TOP BANANA'

Can you help me to learn more?

(Other definitions for top banana that I've seen before include "pick of the bunch?" , "1" , "Big cheese" , "Star comedian" , "leader" .)

I've seen this clue in The Telegraph.
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