—n. 1. Chem. a. any of various bases, the hydroxides of the alkali metals and of ammonium, that neutralize acids to form salts and turn red litmus paper blue.
b. any of various other more or less active bases, as calcium hydroxide.
c. (not in technical use) an alkali metal.
d. Obs.any of various other compounds, as the carbonates of sodium and potassium.
2. Agric.a soluble mineral salt or a mixture of soluble salts, present in some soils, esp. in arid regions, and detrimental to the growing of most crops.