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Meaning of baking powder

bak'ing pow"der

Pronunciation: [key]
  1. any of various powders used as a substitute for yeast in baking, composed of sodium bicarbonate mixed with an acid substance, as cream of tartar, capable of setting carbon dioxide free when the mixture is moistened, causing the dough to rise.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.