Young Arthur is an expert in his trade (7)
I believe the answer is:
artisan
'expert in his trade' is the definition.
'artisan' can be an answer for 'expert' (thesaurus). I am not certain of the 'in his trade' bit.
'young arthur is an' is the wordplay.
'young arthur' becomes 'art' (I've seen this in other clues. I am not sure about the 'young' bit.).
'art'+'is'+'an'='ARTISAN'
Can you help me to learn more?
(Other definitions for artisan that I've seen before include "Train as (anag) - craftsman" , "Skilled worker or craftsman" , "craftsman of his trade" , "man with skill" , "Mechanic" .)