Keyboard player (7)
'keyboard player' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for organist that I've seen before include "It groans for church musician" , "Cathedral musician" , "One plays in church usually" , "Church instr. player" , "Accompanist, keyboard player" .)
'keyboard player' is the definition.
(a piano has a keyboard)
This is the entire clue.
(Other definitions for pianist that I've seen before include "Expert on keys" , "Instrumentalist" , "Key expert" , "Ashkenazy, say" , "Musician" .)