Source : Webster's Revised Unabridged Dictionary (1913)

On \On\, 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:

   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.

            I stood on the bridge at midnight.    --Longfellow.

   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.

            Whosoever shall fall on this stone shall be broken.
                                                  --Matt. xxi.
                                                  44.

   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.

   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.

   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.

   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.

   7. At or in the time of; during; as, on Sunday we abstain
      from labor. See {At} (synonym).

   8. At the time of, conveying some notion of cause or motive;
      as, on public occasions, the officers appear in full dress
      or uniform. Hence, in consequence of, or following; as, on
      the ratification of the treaty, the armies were disbanded.

   9. Toward; for; -- indicating the object of some passion; as,
      have pity or compassion on him.

   10. At the peril of, or for the safety of. ``Hence, on thy
       life.'' --Dryden.

   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.

   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.

             His blood be on us and on our children. --Matt.
                                                  xxvii. 25.

   13. In reference or relation to; as, on our part expect
       punctuality; a satire on society.

   14. Of. [Obs.] ``Be not jealous on me.'' --Shak.

             Or have we eaten on the insane root That takes the
             reason prisoner?                     --Shak.

   Note: Instances of this usage are common in our older
         writers, and are sometimes now heard in illiterate
         speech.

   15. Occupied with; in the performance of; as, only three
       officers are on duty; on a journey.

   16. In the service of; connected with; of the number of; as,
       he is on a newspaper; on a committee.

   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.

   {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.

            They have added the -en plural form on to an elder
            plural.                               --Earle.

            We see the strength of the new movement in the new
            class of ecclesiastics whom it forced on to the
            stage.                                --J. R. Green.

Source : WordNet®

on it
     adv : on that; "text and commentary thereon" [syn: {thereon}, {on
           that}]