The Collaborative International Dictionary of English v.0.48:

Virtue \Vir"tue\ (?; 135), n. [OE. vertu, F. vertu, L. virtus
   strength, courage, excellence, virtue, fr. vir a man. See
   Virile, and cf. Virtu.]
   1. Manly strength or courage; bravery; daring; spirit; valor.
      [Obs.] --Shak.
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            Built too strong
            For force or virtue ever to expugn.   --Chapman.
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   2. Active quality or power; capacity or power adequate to the
      production of a given effect; energy; strength; potency;
      efficacy; as, the virtue of a medicine.
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            Jesus, immediately knowing in himself that virtue
            had gone out of him, turned him about. --Mark v. 30.
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            A man was driven to depend for his security against
            misunderstanding, upon the pure virtue of his
            syntax.                               --De Quincey.
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            The virtue of his midnight agony.     --Keble.
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   3. Energy or influence operating without contact of the
      material or sensible substance.
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            She moves the body which she doth possess,
            Yet no part toucheth, but by virtue's touch. --Sir.
                                                  J. Davies.
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   4. Excellence; value; merit; meritoriousness; worth.
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            I made virtue of necessity.           --Chaucer.
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            In the Greek poets, . . . the economy of poems is
            better observed than in Terence, who thought the
            sole grace and virtue of their fable the sticking in
            of sentences.                         --B. Jonson.
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   5. Specifically, moral excellence; integrity of character;
      purity of soul; performance of duty.
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            Virtue only makes our bliss below.    --Pope.
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            If there's Power above us,
            And that there is all nature cries aloud
            Through all her works, he must delight in virtue.
                                                  --Addison.
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   6. A particular moral excellence; as, the virtue of
      temperance, of charity, etc. "The very virtue of
      compassion." --Shak. "Remember all his virtues."
      --Addison.
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   7. Specifically: Chastity; purity; especially, the chastity
      of women; virginity.
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            H. I believe the girl has virtue.
            M. And if she has, I should be the last man in the
            world to attempt to corrupt it.       --Goldsmith.
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   8. pl. One of the orders of the celestial hierarchy.
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            Thrones, dominations, princedoms, virtues, powers.
                                                  --Milton.
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   Cardinal virtues. See under Cardinal, a.

   In virtue of, or By virtue of, through the force of; by
      authority of. "He used to travel through Greece by virtue
      of this fable, which procured him reception in all the
      towns." --Addison. "This they shall attain, partly in
      virtue of the promise made by God, and partly in virtue of
      piety." --Atterbury.

   Theological virtues, the three virtues, faith, hope, and
      charity. See --1 Cor. xiii. 13.
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Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "by virtue of":
   after, because of, by, by authority of, by dint of, by means of,
   by reason of, by use of, by way of, considering, due to, hereby,
   herewith, in consideration of, in view of, in virtue of, on,
   on account of, owing to, per, thanks to, thereby, therewith,
   through, upon, via, whereby, wherewith, wherewithal, with