Plead for three keys (3)
I believe the answer is:
beg
'plead for' is the definition.
(thesaurus)
'three keys' is the wordplay.
'three keys' means three replacements for 'key'.
'key' becomes 'b' (eg B major, musical key).
'key' becomes 'e' (a musical key).
'key' becomes 'g' (musical key).
'b'+'e'+'g'='BEG'
(Other definitions for beg that I've seen before include "Plead or importune" , "Plead or scrounge" , "Implore or cadge" , "Earnestly entreat" , "Get by any means - . . ., borrow or steal" .)