Bachelor, on last in show, makes a drink (4)
I believe the answer is:
brew
'a drink' is the definition.
(brew is a kind of drink)
'bachelor on last in show' is the wordplay.
'bachelor' becomes 'b' (abbreviation e.g. BA=Bachelor of Arts).
'on' becomes 're' ('on' can be mean 'with reference to'**).
'last in' suggests the final letters.
The last letter of 'show' is 'w'.
'b'+'re'+'w'='BREW'
'makes' acts as a link.
(Other definitions for brew that I've seen before include "Plot" , "Ferment, concoct" , "Make beer; drink of tea" , "Make beer by boiling and fermentation" , "Concoction" .)