By getting a half of beer on the quiet (3)
I believe the answer is:
per
'by' is the definition.
(I've seen this in another clue)
'a half of beer on the quiet' is the wordplay.
'a half of' means to take half the letters.
'on' says to put letters next to each other.
'the quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'beer' cut in half 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" .)