[1] : The Collaborative International Dictionary of English v.0.48

vain \vain\ v=an, 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.
      1913 webster

            every man walketh in a vain show.     --ps. xxxix.
                                                  6.
      1913 webster

            let no man deceive you with vain words. --eph. v. 6.
      1913 webster

            vain pomp, and glory of this world, i hate ye
                                                  --shak.
      1913 webster

            vain wisdom all, and false philosophy. --milton.
      1913 webster

   2. destitute of force or efficacy; effecting no purpose;
      fruitless; ineffectual; as, vain toil; a vain attempt.
      1913 webster

            bring no more vain oblations.         --isa. i. 13.
      1913 webster

            vain is the force of man
            to crush the pillars which the pile sustain.
                                                  --dryden.
      1913 webster

   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.
      1913 webster

            but wilt thou know, o vain man, that faith apart
            from works is barren?                 --james ii. 20
                                                  rev. ver..
      1913 webster

            the minstrels played on every side,
            vain of their art.                    --dryden.
      1913 webster

   4. showy; ostentatious.
      1913 webster

            load some vain church with old theatric state.
                                                  --pope.
      1913 webster

   syn: empty; worthless; fruitless; ineffectual; idle; unreal;
        shadowy; showy; ostentatious; light; inconstant;
        deceitful; delusive; unimportant; trifling.
        1913 webster
see also:
vainer vainest vanish vanity vaunt 

[2] : The Collaborative International Dictionary of English v.0.48

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

   in vain.
      1913 webster

   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.
      1913 webster
see also:
in vain for vain in vain to take the name of god in vain 

[3] : WordNet (r) 2.0

vain
     adj 1: characteristic of false pride; having an exaggerated sense
            of self-importance; "a conceited fool"; "an attitude
            of self-conceited arrogance"; "an egotistical
            disregard of others"; "so swollen by victory that he
            was unfit for normal duty"; "growing ever more
            swollen-headed and arbitrary"; "vain about her
            clothes" syn: conceited, egotistic, egotistical,
             self-conceited, swollen, swollen-headed
     2: unproductive of success; "a fruitless search"; "futile years
        after her artistic peak"; "a sleeveless errand"; "a vain
        attempt" syn: bootless, fruitless, futile, sleeveless
see also:
conceited egotistic egotistical self-conceited swollen swollen-headed 
bootless fruitless futile sleeveless 

[4] : Moby Thesaurus II by Grady Ward, 1.0

147 moby thesaurus words for "vain":
   gascon, abortive, absurd, airy, arrogant, asinine, barren,
   baseless, boastful, boasting, bootless, bootlessly, braggart,
   bragging, catchpenny, cocky, complacent, conceited, consequential,
   counterproductive, coxcombical, dandyish, delusive, delusory,
   doomed, effete, egocentric, egoistic, egotistical, empty,
   etiolated, fanfaron, fanfaronading, fatuitous, fatuous, feckless,
   flimsy, foolish, foppish, foredoomed, fribble, fribbling,
   frivolous, frothy, fruitless, fruitlessly, futile, futilely,
   gasconading, groundless, haughty, hollow, idle, ill-founded,
   improperly, in vain, inadequate, inane, ineffective, ineffectual,
   inefficacious, inoperative, invalid, light, misleading, narcissan,
   narcissine, narcissistic, narcistic, nugacious, nugatory,
   of no force, otiose, overproud, overweening, paltry, petty,
   pointless, profitless, proud, puny, self-admiring,
   self-advertising, self-applauding, self-approving, self-assuming,
   self-complacent, self-conceited, self-congratulating,
   self-congratulatory, self-content, self-contented, self-delighting,
   self-endeared, self-esteeming, self-flattering, self-glorious,
   self-gratulating, self-gratulatory, self-important, self-lauding,
   self-loving, self-respecting, self-satisfied, self-sufficient,
   self-vaunting, shallow, silly, slender, slight, smug, sterile,
   stuck-up, superficial, thrasonic, thrasonical, trifling, trite,
   trivial, unavailable, unavailing, unbased, unfounded, ungrounded,
   unproductive, unprofitable, unsuccessful, unsuccessfully,
   unsupportable, unsupported, unsustainable, unsustained, untenable,
   unwarranted, useless, vacuous, vainglorious, vainly, valueless,
   vapid, vaporing, vaunting, void, windy, without basis,
   without foundation, worthless

Vain >> V Words
Vain, definition of term: Vain
vain_pag1.html

In Vain >> I Words
In Vain, definition of term: In Vain
in+vain_pag1.html