Ordinarily we apply this word to rich vegetation that luxuriously covers an area. What could that possibly have in common with someone who never thinks of water when thirsty? Not much, other than that plants and people who are potted may both sway in the breeze.
Lush in the alcoholic sense --in Britain it means the drinks themselves --most likely comes from an English brewer whose name was Lushington. In the 19th century a number of actors who frequented a particular London tavern even referred to themselves as “The City of Lushington.”
Lush may also have some connection to the Old French expression, vin lousch, meaning thick wine. Drunks sound like they have a mouthful of it when they speak.
Source: Brewer’s Dictionary of Phrase and Fable, 16e (Brewer’s Dictionary of Phrase and Fable) edited by Adriam Room
