Yours truly has played clarinet in commercial (10)
I believe the answer is:
mercantile
'commercial' is the definition.
(similar in meaning)
'yours truly has played clarinet' is the wordplay.
'yours truly' becomes 'me' (the person who set this crossword).
'has' means one lot of letters goes inside another.
'played' is an anagram indicator (letters playing around).
'clarinet' with letters rearranged gives 'ercantil'.
'me' enclosing 'ercantil' is 'MERCANTILE'.
'in' acts as a link.
(Other definitions for mercantile that I've seen before include "Relating to (overseas) trade" , "concerning trade" , "Commercial" , "Dealing with trade" , "Relating to trade or commerce" .)