The Collaborative International Dictionary of English v.0.48:

Vain \Vain\ (v[=a]n), a. [Compar. Vainer; superl. Vainest.]
   [F. vain, L. vanus empty, void, vain. Cf. Vanish, Vanity,
   Vaunt to boast.]
   1. Having no real substance, value, or importance; empty;
      void; worthless; unsatisfying. "Thy vain excuse." --Shak.
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            Every man walketh in a vain show.     --Ps. xxxix.
                                                  6.
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            Let no man deceive you with vain words. --Eph. v. 6.
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            Vain pomp, and glory of this world, I hate ye!
                                                  --Shak.
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            Vain wisdom all, and false philosophy. --Milton.
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   2. Destitute of force or efficacy; effecting no purpose;
      fruitless; ineffectual; as, vain toil; a vain attempt.
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            Bring no more vain oblations.         --Isa. i. 13.
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            Vain is the force of man
            To crush the pillars which the pile sustain.
                                                  --Dryden.
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   3. Proud of petty things, or of trifling attainments; having
      a high opinion of one's own accomplishments with slight
      reason; conceited; puffed up; inflated.
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            But wilt thou know, O vain man, that faith apart
            from works is barren?                 --James ii. 20
                                                  (Rev. Ver.).
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            The minstrels played on every side,
            Vain of their art.                    --Dryden.
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   4. Showy; ostentatious.
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            Load some vain church with old theatric state.
                                                  --Pope.
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   Syn: Empty; worthless; fruitless; ineffectual; idle; unreal;
        shadowy; showy; ostentatious; light; inconstant;
        deceitful; delusive; unimportant; trifling.
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