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.]
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.