The word vain, according the first definition found in the OED, means, “Devoid of real value, worth, or significance; idle, unprofitable, useless, worthless; of no effect, force, or power; fruitless, futile, unavailing. The earliest recording of the word vain comes from Cursor M. in 1300: “Quen idel thought me come and vain, Wit will I stode pam noght again.” The sub definition to this first one is, “of material things: useless, worthless.” The second definition of the word vain is, “Empty, vacant, void.” So, if you call someone vain – you could be calling the worthless – or go even deeper and be calling them empty or void of something. The third definition is more specifically used to describe people. It states, “of persons: devoid of sense of wisdom; foolish, silly thoughtless; of an idle or futile nature or disposition.” According to the OED, this definition is rare. It was last used in 1819 by Shelley who wrote, “So that our hair should seep the footsteps of the vain and senseless crowd.” The fourth definition of vain is the one that we all are used to hearing and think of when we hear this word. Vain means, “given to or indulging in personal vanity; having an excessively high opinion of one’s own appearance, attainments, qualities, possessions, etc.; delighting in, or desirous of attracting, the admiration of others; conceited.” We’ve also all probably heard the fifth definition of the word vain as well. The fifth definition is the adverb phrase in vain, which means, “to no effect or purpose; ineffectually, uselessly, vainly.” A famous line from several movies (that I can’t actually name off the top of my head) is something along the lines of, “I won’t let him die in vain.” The last example recorded in the OED comes from Bryce Holy Rom. Emp. In 1864: “Lewis tried in vain to satisfy his sons . . . by dividing and redividing.” The sixth definition is a lot like the latter, but instead of something having no purpose, this definition is, “to take . . . in vain: to disregard, to treat with contempt.” The best example I could think of – that just so happens to be in the OED as a sub definition – is to take the LORDS name in vain. The sub definition is as follows: “With name as object. To use or utter (the name of God) lightly, needlessly, or profanely; transf. to mention or speak of casually or idly.” The final full definition of the word vain means, “vanity; a vain thing.” The sub definition of this means, “Emptiness; void of space.” So, I believe this last definition sort of encompasses many of the definitions before it.