Graduate and lieutenant making whisky (4)
I believe the answer is:
malt
'whisky' is the definition.
(malt whisky is a kind of whisky)
'graduate and lieutenant' is the wordplay.
'graduate' becomes 'ma' (abbreviation for Master of Arts**).
'and' means one lot of letters go next to another.
'lieutenant' becomes 'lt'.
'ma'+'lt'='MALT'
'making' acts as a link.
(Other definitions for malt that I've seen before include "Whisky ingredient" , "Barley product used in brewing" , "strong drink" , "Dried grain used for brewing and distilling" , "Cereal grain for distilling" .)