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.

Source: Webster's Revised Unabridged Dictionary (1913)