Profound notes on record (4)
I believe the answer is:
deep
'profound' is the definition.
(similar in meaning)
'notes on record' is the wordplay.
'notes' becomes 'de' (two musical notes).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'record' becomes 'EP' (abbreviation for extended play record).
'de'+'ep'='DEEP'
(Other definitions for deep that I've seen before include "Profound - cunning - sea - bass" , "Extending far down" , "Heartfelt" , "profoundly" , "Mysterious" .)