Whisky misuse is reduced by half (4)
I believe the answer is:
malt
'whisky' is the definition.
(malt whisky is a kind of whisky)
'misuse is reduced by half' is the wordplay.
'is reduced' says to take the initial letters (the word is reduced to its first letter).
'by half' becomes 'alt' (I can't explain this - if you can you should believe this answer much more).
The initial letter of 'misuse' is 'm'.
'm'+'alt'='MALT'
Can you help me to learn more?
(Other definitions for malt that I've seen before include "Grain product used in beer and whisky" , "Grain prepared for brewing or distilling" , "Brewing material" , "strong drink" , "Pure whisky" .)