An alkoxide is the conjugate base of an alcohol : methoxide , ethoxide , tert-butoxide . Alkoxides are strong bases and good nucleophiles.
Examples
Example 22.5 (An unsymmetrical ether)
2-Methoxy-2-methylpropane (methyl tert-butyl ether): sodium tert-butoxide with iodomethane gives it cleanly; sodium methoxide with the tertiary bromide, 2-bromo-2-methylpropane, gives 2-methylpropene by E2. Bulky on the alkoxide side, small on the halide side.