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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1.) People have tried for years to copy the seasoning recipe for Kentucky Fried Chicken to no avail. Colonel Sanders' SECRET INGREDIENT is worth millions.

3.) "I didn't work at Burger King for long, but if I ever saw a cop ordering a hamburger I always made sure it was a booger burger if I could get away with spittin' my SECRET INGREDIENT on the pickles.
by Bongo Cholomongo September 21, 2006
to add to a food or item.
1)i added a secret ingredient. its love....my love

2)do these brownies have any secret ingredients???
by Doug...H October 22, 2005