intervene

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To come, appear, or lie between two things: You can't see the lake from there because the house intervenes.
2. v. To come or occur between two periods or points of time: A year intervened between the two dynasties.
3. v. To occur as an extraneous or unplanned circumstance: He would have his degree by now if his laziness hadn't intervened.
4. v. To involve oneself in a situation so as to alter or hinder an action or development: "Every gardener faces choices about how and how much to intervene in nature's processes” ( Dora Galitzki).
5. v. To interfere, usually through force or threat of force, in the affairs of another nation.
6. v. Law To enter into a suit as a third party for one's own interests.

Century Dictionary and Cyclopedia

1. To come between; fall or happen between things, persons, periods, or events; be intermediate, or appear or happen intermediately.
2. To come between in act; act intermediately or mediatorially; interfere or interpose, as between persons, parties, or states.
3. In law, to interpose and become a party to a suit pending between other parties: as, stockholders may intervene in a suit against directors.
4. To come between; divide.
5. n. A coming together; a meeting.

Wiktionary

1. v. To come between, or to be between, persons or things; -- followed by between; as, the Mediterranean intervenes between Europe and Africa.
2. v. 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. v. To interpose; as, to intervene to settle a quarrel; get involved, so as to alter or hinder an action
4. v. law 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.

GNU Webster's 1913

1. v. To come between, or to be between, persons or things; -- followed by between.
2. v. To occur, fall, or come between, points of time, or events
3. v. To interpose.
4. v. 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.
5. v. rare To come between.
6. n. obsolete A coming between; intervention; meeting.

WordNet 3.0

1. v. be placed or located between other things or extend between spaces and events
2. v. occur between other event or between certain points of time
3. v. get involved, so as to alter or hinder an action, or through force or threat of force