(Proverbs 25:20; R.V. marg., "soda"), properly "natron," a substance so called because, rising from the bottom of the Lake Natron in Egypt, it becomes dry and hard in the sun, and is the soda which effervesces when vinegar is poured on it. It is a carbonate of soda, not saltpetre, which the word generally denotes (Jeremiah 2:22; R.V. "lye").

Noah Webster's New International Dictionary of the English Language

1. (n.) A white crystalline semitransparent salt; potassium nitrate; saltpeter. See Saltpeter.

2. (n.) Native sodium carbonate; natron.

3. (n.) See Niter.