The Collaborative International Dictionary of English v.0.48:

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.]
   [1913 Webster]
   1. To come between, or to be between, persons or things; --
      followed by between; as, the Mediterranean intervenes
      between Europe and Africa.
      [1913 Webster]

   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.
      [1913 Webster]

   3. To interpose; as, to intervene to settle a quarrel.
      [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Intervene \In`ter*vene"\, v. t.
   To come between. [R.]
   [1913 Webster]

         Self-sown woodlands of birch, alder, etc., intervening
         the different estates.                   --De Quincey.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Intervene \In`ter*vene"\, n.
   A coming between; intervention; meeting. [Obs.] --Sir H.
   Wotton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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: intervene, 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"

Moby Thesaurus II by Grady Ward, 1.0:

136 Moby Thesaurus words for "intervene":
   act between, arbitrate, arrest, bargain, barge in, bottle up,
   break, break in, break in upon, burst in, butt in, call a break,
   call time, charge in, check, come between, countercheck, crash,
   crash in, crash the gates, creep in, crowd in, curb, cut in,
   dam up, damp, dampen, declare a recess, delay, detain, divide,
   drag in, edge in, elapse, elbow in, encroach, entrench, foist in,
   fudge in, go between, hinder, hold back, hold in check, hold up,
   horn in, impede, impinge, implant in, impose, impose on,
   impose upon, infiltrate, infringe, inhibit, inject in, insert in,
   insinuate, insinuate in, intercalate, intercede, intercept,
   interfere, interjaculate, interject, interlope, interlude,
   intermeddle, intermediate, intermit, interpolate, interpose,
   interrupt, interval, introduce in, intrude, invade, irrupt, judge,
   keep back, keep in check, lug in, make terms, meddle, mediate,
   meet halfway, moderate, negotiate, obtrude, oppose, part, pass,
   pause, press in, push in, put between, put on, put upon, recess,
   referee, represent, repress, resist, restrain, retard, run in,
   rush in, sandwich, scotch, separate, set back, sever, slacken,
   slink in, slip in, smash in, smuggle in, sneak in, snub,
   squeeze in, steal in, step in, storm in, suppress, take a break,
   take five, take ten, throng in, throw in, thrust in, treat with,
   trench, trespass, umpire, wedge in, work in, worm in