Source : Webster's Revised Unabridged Dictionary (1913)

Intervene \In`ter*vene"\, v. i. [imp. & p. p. {Intervened}; p.
   pr. & vb. n. {Intervening}.] [L. intervenire, interventum, to
   intervene, to hinder; inter between + venire to come; akin to
   E. come: cf. F. intervenir. See {Come}.]
   1. To come between, or to be between, persons or things; --
      followed by between; as, the Mediterranean intervenes
      between Europe and Africa.

   2. To occur, fall, or come between, points of time, or
      events; as, an instant intervened between the flash and
      the report; nothing intervened ( i. e., between the
      intention and the execution) to prevent the undertaking.

   3. To interpose; as, to intervene to settle a quarrel.

   4. In a suit to which one has not been made a party, to put
      forward a defense of one's interest in the subject matter.
      --Abbott.

Intervene \In`ter*vene"\, v. t.
   To come between. [R.]

         Self-sown woodlands of birch, alder, etc., intervening
         the different estates.                   --De Quincey.

Intervene \In`ter*vene"\, n.
   A coming between; intervention; meeting. [Obs.] --Sir H.
   Wotton.

Source : WordNet®

intervene
     v 1: 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: {step in}, {interfere},
           {interpose}]
     2: be placed or located between other things or extend between
        spaces and events; "This interludes intervenes between the
        two movements"; "Eight days intervened"
     3: occur between other event or between certain points of time;
        "the war intervened between the birth of her two children"