The Collaborative International Dictionary of English v.0.48:

On \On\ ([o^]n), prep. [OE. on, an, o, a, AS. on, an; akin to D.
   aan, OS. & G. an, OHG. ana, Icel. [=a], Sw. [*a], Goth. ana,
   Russ. na, L. an-, in anhelare to pant, Gr. 'ana`, Zend ana.
   [root]195. Cf. A-, 1, Ana-, Anon.]
   The general signification of on is situation, motion, or
   condition with respect to contact or support beneath; as:
   [1913 Webster]

   1. At, or in contact with, the surface or upper part of a
      thing, and supported by it; placed or lying in contact
      with the surface; as, the book lies on the table, which
      stands on the floor of a house on an island.
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            I stood on the bridge at midnight.    --Longfellow.
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   2. To or against the surface of; -- used to indicate the
      motion of a thing as coming or falling to the surface of
      another; as, rain falls on the earth.
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            Whosoever shall fall on this stone shall be broken.
                                                  --Matt. xxi.
                                                  44.
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   3. Denoting performance or action by contact with the
      surface, upper part, or outside of anything; hence, by
      means of; with; as, to play on a violin or piano. Hence,
      figuratively, to work on one's feelings; to make an
      impression on the mind.
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   4. At or near; adjacent to; -- indicating situation, place,
      or position; as, on the one hand, on the other hand; the
      fleet is on the American coast.
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   5. In addition to; besides; -- indicating multiplication or
      succession in a series; as, heaps on heaps; mischief on
      mischief; loss on loss; thought on thought. --Shak.
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   6. Indicating dependence or reliance; with confidence in; as,
      to depend on a person for assistance; to rely on; hence,
      indicating the ground or support of anything; as, he will
      promise on certain conditions; to bet on a horse; based on
      certain assumptions.
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   7. At or in the time of; during; as, on Sunday we abstain
      from labor. See At (synonym).
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   8. At the time of; -- often conveying some notion of cause or
      motive; as, on public occasions, the officers appear in
      full dress or uniform; the shop is closed on Sundays.
      Hence, in consequence of, or following; as, on the
      ratification of the treaty, the armies were disbanded;
      start on the count of three.
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   9. Toward; for; -- indicating the object of some passion; as,
      have pity or compassion on him.
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   10. At the peril of, or for the safety of. "Hence, on thy
       life." --Dryden.
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   11. By virtue of; with the pledge of; -- denoting a pledge or
       engagement, and put before the thing pledged; as, he
       affirmed or promised on his word, or on his honor.
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   12. To the account of; -- denoting imprecation or invocation,
       or coming to, falling, or resting upon; as, on us be all
       the blame; a curse on him.
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             His blood be on us and on our children. --Matt.
                                                  xxvii. 25.
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   13. In reference or relation to; as, on our part expect
       punctuality; a satire on society.
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   14. Of. [Obs.] "Be not jealous on me." --Shak.
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             Or have we eaten on the insane root
             That takes the reason prisoner?      --Shak.
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   Note: Instances of this usage are common in our older
         writers, and are sometimes now heard in illiterate
         speech.
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   15. Occupied with; in the performance of; as, only three
       officers are on duty; on a journey; on the job; on an
       assignment; on a case; on the alert.
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   16. In the service of; connected with; a member of; as, he is
       on a newspaper; on a committee.
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   Note: On and upon are in general interchangeable. In some
         applications upon is more euphonious, and is therefore
         to be preferred; but in most cases on is preferable.
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   17. In reference to; about; concerning; as, to think on it;
       to meditate on it.
       [PJC]

   On a bowline. (Naut.) Same as Closehauled.

   On a wind, or On the wind (Naut.), sailing closehauled.


   On a sudden. See under Sudden.

   On board, On draught, On fire, etc. See under Board,
      Draught, Fire, etc.

   On it, On't, of it. [Obs. or Colloq.] --Shak.

   On shore, on land; to the shore.

   On the road, On the way, On the wing, etc. See under
      Road, Way, etc.

   On to, upon; on; to; -- sometimes written as one word,
      onto, and usually called a colloquialism; but it may be
      regarded in analogy with into.
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            They have added the -en plural form on to an elder
            plural.                               --Earle.
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            We see the strength of the new movement in the new
            class of ecclesiastics whom it forced on to the
            stage.                                --J. R. Green.
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Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "on to":
   alive to, appreciative of, apprised of, awake to, aware of,
   behind the curtain, behind the scenes, cognizant of, conscious of,
   hep to, in the know, in the secret, informed of, let into,
   mindful of, no stranger to, privy to, seized of, sensible of,
   sensible to, streetwise, undeceived, wise to