In speech, expresses disapproval of alcohol (5)
I believe the answer is:
booze
'alcohol' is the definition.
(I know that alcohol can be written as booze)
'in speech expresses disapproval' is the wordplay.
'in speech' indicates a 'sounds like' (homophone) clue.
'expresses disapproval' becomes 'boos' (to boo someone is to express disapproval with them).
'boos' sounds like 'BOOZE'.
'of' acts as a link.
(Other definitions for booze that I've seen before include "Consume alcohol" , "Drink heavily" , "Alcohol (sl.)" , "Drink to excess (colloq.)" , "plonk?" .)