a) Abstaining from drinking any alcoholic drink, usually in the sense of having given it up (as opposed to never having partaken).
1917: “Thank you, but; – er – I’m on the wagon, you know,” declined the youth. — , The Oakdale Affair [
b) By extension, maintaining a program of self-improvement or abstinence from some other undesirable habit.
He’s been on the smoking cessation wagon for two weeks now.
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