Source : Webster's Revised Unabridged Dictionary (1913)

Vain \Vain\, n.
   Vanity; emptiness; -- now used only in the phrase in vain.

   {For vain}. See {In vain}. [Obs.] --Shak.

   {In vain}, to no purpose; without effect; ineffectually. ``
      In vain doth valor bleed.'' --Milton. `` In vain they do
      worship me.'' --Matt. xv. 9.

   {To take the name of God in vain}, to use the name of God
      with levity or profaneness.