Plead for three notes (3)
I believe the answer is:
beg
'plead for' is the definition.
(thesaurus)
'three notes' is the wordplay.
'three notes' can mean three substitutions for 'note'.
'note' becomes 'b' (musical note).
'note' becomes 'e' (musical note).
'note' becomes 'g' (musical note).
'b'+'e'+'g'='BEG'
(Other definitions for beg that I've seen before include "Earnestly entreat" , "Plead or ask for alms" , "Ask humbly" , "Plead or scrounge" , "Beseech or ask for charity" .)