The Collaborative International Dictionary of English v.0.48:

Against \A*gainst"\ (?; 277), prep. [OE. agens, ageynes, AS.
   ongegn. The s is adverbial, orig. a genitive ending. See
   Again.]
   1. Abreast; opposite to; facing; towards; as, against the
      mouth of a river; -- in this sense often preceded by over.
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            Jacob saw the angels of God come against him.
                                                  --Tyndale.
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   2. From an opposite direction so as to strike or come in
      contact with; in contact with; upon; as, hail beats
      against the roof.
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   3. In opposition to, whether the opposition is of sentiment
      or of action; on the other side; counter to; in
      contrariety to; hence, adverse to; as, against reason;
      against law; to run a race against time.
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            The gate would have been shut against her.
                                                  --Fielding.
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            An argument against the use of steam. --Tyndale.
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   4. By of before the time that; in preparation for; so as to
      be ready for the time when. [Archaic or Dial.]
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            Urijah the priest made it, against King Ahaz came
            from Damascus.                        --2 Kings xvi.
                                                  11.
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   Against the sun, in a direction contrary to that in which
      the sun appears to move.
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Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "against":
   about, across, adverse to, as to, at cross-purposes with, athwart,
   con, concerning, confronting, contra, contrary to, counter to,
   dead against, despite, en route to, facing, for, fronting,
   headed for, in conflict with, in contact with, in contempt of,
   in defiance of, in disagreement with, in front of,
   in opposition to, in order to, in passage to, in preparation for,
   in spite of, in transit to, next to, on, on route to, opposed to,
   opposite, opposite to, over against, re, regardless of, respecting,
   to, touching, toward, towards, up, up against, upon, versus,
   vis-a-vis, with respect to