The word punch means five, originating from the Hindustani word panch. Punch Day sadly isn’t an excuse to drink five glasses of punch; rather, it celebrates the traditional punch base recipe of five key ingredients, which most punches still use – alcohol (usually spirits), lemon (or other fruits), sugar, water, and tea (or other spices, e.g. cinnamon).
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All details taken directly from provider content at http://www.daysoftheyear.com/days/punch-day/