1. Any of various typically water-soluble and bitter tasting compounds that in solution have a pH greater than 7, are capable of reacting with an acid to form a salt, and are molecules or ions able to take up a proton from an acid or able to give up an unshared pair of electrons to an acid.
  2. Chemicals that release hydroxide ions (OH–) in solution. Such solutions have a soapy feel, neutralize acids, and conduct electricity.