Musician possibly sang with trio (8)
I believe the answer is:
organist
'musician' is the definition.
(I know that organist is a type of musician)
'possibly sang with trio' is the wordplay.
'possibly' indicates anagramming the letters.
'with' is a charade indicator (letters next to each other).
'sang' after 'trio' is 'triosang'.
'triosang' with letters rearranged gives 'ORGANIST'.
(Other definitions for organist that I've seen before include "Accompanist, keyboard player" , "Church instr. player" , "Cathedral musician" , "It groans for church musician" , "One plays in church usually" .)