The Collaborative International Dictionary of English v.0.48:

Vanquish \Van"quish\ (v[a^][ng]"kw[i^]sh), v. t. [imp. & p. p.
   Vanquished (v[a^][ng]"kw[i^]sht); p. pr. & vb. n.
   Vanquishing.] [OE. venquishen, venquissen, venkisen, F.
   vaincre, pret. vainquis, OF. veintre, pret. venqui, venquis
   (cf. an OF. infin. vainquir), fr. L. vincere; akin to AS.
   w[imac]g war, battle, w[imac]gend a warrior, w[imac]gan to
   contend, fight, OHG. w[imac]gant a warrior, w[imac]gan to
   fight, Icel. v[imac]g battle, Goth. weihan to fight, contend.
   Cf. Convince, Evict, Invincible, Victor.]
   1. To conquer, overcome, or subdue in battle, as an enemy.
      --Hakluyt.
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            They . . . vanquished the rebels in all encounters.
                                                  --Clarendon.
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   2. Hence, to defeat in any contest; to get the better of; to
      put down; to refute.
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            This bold assertion has been fully vanquished in a
            late reply to the Bishop of Meaux's treatise.
                                                  --Atterbury.
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            For e'en though vanquished, he could argue still.
                                                  --Goldsmith.
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   Syn: To conquer; surmount; overcome; confute; silence. See
        Conquer.
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