Pilot Officer grabs Scotsman softly (5)
I believe the answer is:
piano
'softly' is the definition.
(musical term for softly or quietly)
'pilot officer grabs scotsman' is the wordplay.
'pilot officer' becomes 'po' (short for pilot officer).
'grabs' is an insertion indicator.
'scotsman' becomes 'ian' (common Scottish name).
'po' enclosing 'ian' is 'PIANO'.
(Other definitions for piano that I've seen before include "Keyboard instrument" , "key holder" , "Upright type?" , "In musical notation, this means softly" , "one of 6 [STEINWAYS]" .)