By getting a half of beer on the quiet (3)
I believe the answer is:
per
'by' is the definition.
(thesaurus)
'a half of beer on the quiet' is the wordplay.
'a half of' means to take half the letters.
'on' is a charade indicator (letters next to each other).
'the quiet' becomes 'p' (music symbol for 'piano').
'beer' halved is 'er'.
'er' after 'p' is 'PER'.
'getting' acts as a link.
(Other definitions for per that I've seen before include "Preposition meaning for each" , "According to" , "Preposition indicating by means of" , "For each or every" .)