Drink cheat — one who should avoid booze? (11)
I believe the answer is:
screwdriver
'drink' is the definition.
(screwdriver is a kind of drink)
'cheat one who should avoid booze?' is the wordplay.
'cheat' becomes 'screw' (synonyms).
'one who should avoid booze?' becomes 'driver' (don't drink and drive).
'screw'+'driver'='SCREWDRIVER'
(Other definitions for screwdriver that I've seen before include "Tool for turning fastening device" , "Drink" , "Vodka/orange cocktail" , "Cocktail (vodka and 4 down juice)" , "Common tool" .)