1.) The part of the recipe that is protected by
lock and key so no one will copy the success of such a perfect concoction. Usually the SECRET INGREDIENT is what distinguishes the original article from phony wannabes, look-alikes and knock-offs similarly to the effect of "special sauce".
2.) Euphemism for something (anything) added to the mix (or to the
take-out food order) that's not supposed to be in there. Added to accomplish crafty revenge, the SECRET INGREDIENT is usually undetected. But there's
hell to pay if one is caught.
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