Source : Webster's Revised Unabridged Dictionary (1913)

Purpose \Pur"pose\, n. [OF. purpos, pourpos, propos, L.
   propositum. See {Propound}.]
   1. That which a person sets before himself as an object to be
      reached or accomplished; the end or aim to which the view
      is directed in any plan, measure, or exertion; view; aim;
      design; intention; plan.

            He will his firste purpos modify.     --Chaucer.

            As my eternal purpose hath decreed.   -- Milton.

            The flighty purpose never is o'ertook Unless the
            deed go with it.                      --Shak.

   2. Proposal to another; discourse. [Obs.] --Spenser.

   3. Instance; example. [Obs.] --L'Estrange.

   {In purpose}, {Of purpose}, {On purpose}, with previous
      design; with the mind directed to that object;
      intentionally. On purpose is the form now generally used.

   Syn: design; end; intention; aim. See {Design}.

Source : WordNet®

on purpose
     adv : with intention; in an intentional manner; "he used that word
           intentionally"; "I did this by choice" [syn: {intentionally},
            {deliberately}, {designedly}, {purposely}, {advisedly},
            {by choice}, {by design}] [ant: {by chance}, {unintentionally},
            {unintentionally}]