Source : Webster's Revised Unabridged Dictionary (1913)

Interpose \In`ter*pose"\, v. t. [imp. & p. p. {Interposed}; p.
   pr. & vb. n. {Interposing}.] [F. interposer. See {Inter-},
   and {Pose}, v. t.]
   1. To place between; as, to interpose a screen between the
      eye and the light.

            Mountains interposed Make enemies of nations.
                                                  --Cowper.

   2. To thrust; to intrude; to between, either for aid or for
      troubling.

            What watchful cares do interpose themselves Betwixt
            your eyes and night?                  --Shak.

            The common Father of mankind seasonably interposed
            his hand, and rescues miserable man.  --Woodward.

   3. To introduce or inject between the parts of a conversation
      or argument. --Milton.

Interpose \In`ter*pose"\, v. i.
   1. To be or come between.

            Long hid by interposing hill or wood. --Cowper.

   2. To step in between parties at variance; to mediate; as,
      the prince interposed and made peace. --Pope.

   3. To utter a sentiment by way of interruption. --Boyle.

   Syn: To intervene; intercede; mediate; interfere;
        intermeddle.

   Usage: To {Interpose}, {Intermeddle}, {Interfere}. A man may
          often interpose with propriety in the concerns of
          others; he can never intermeddle without being
          impertinent or officious; nor can be interfere without
          being liable to the same charge, unless he has rights
          which are interfered with. ``In our practical use,
          interference is something offensive. It is the pushing
          in of himself between two parties on the part of a
          third who was not asked, and is not thanked for his
          pains, and who, as the feeling of the word implies,
          had no business there; while interposition is employed
          to express the friendly, peacemaking mediation of one
          whom the act well became, and who, even if he was not
          specially invited thereunto, is still thanked for what
          he has done.'' --Trench.

Interpose \In"ter*pose\, n.
   Interposition. [Obs.]

Source : WordNet®

interpose
     v 1: be or come between; "An interposing thicket blocked their
          way"
     2: introduce; "God interposed death"
     3: to insert between other elements; "She interjected clever
        remarks" [syn: {interject}, {come in}, {put in}, {throw in},
         {inject}]
     4: get involved, so as to alter or hinder an action, or through
        force or threat of force; "Why did the U.S. not intervene
        earlier in WW II?" [syn: {intervene}, {step in}, {interfere}]