intervene

verb

Etymology: Back-formation from intervention, and/or from Latin interveniō (“come between”, verb).

1. To become involved in a situation, so as to alter or prevent an action.

   “The police had to be called to intervene in the fight.”

   “Nature film-makers are discouraged from intervening in the events they are attempting to capture on film.”

2. To occur, fall, or come between, points of time, or events.

   “An instant intervened between the flash and the report.”

   “[…] it is plain, that shaking off a Power, which Force, and not Right, hath set over any one, though it hath the Name of Rebellion; yet is no Offence before God, but that which he allows and countenances, though even Promises and Covenants, when obtain’d by force, have intervened.”

3. To occur or act as an obstacle or delay.

   “Nothing intervened to prevent the undertaking.”

   “The weather intervened before the contest could get under way.”

4. To say (something) in the middle of a conversation or discussion between other people, or to respond to a situation involving other people.

   “Young Scarfe stared, astounded. “You haven’t met before,” Mrs. Gould intervened. “Mr. Decoud—Mr. Scarfe.””

   ““That sounds suspiciously like bigotry to me,” intervened Maitland, sweetening his impertinence with a dimpled smile.”

5. To come between, or to be between, persons or things.

   “The Mediterranean intervenes between Europe and Africa.”

   “1668, Joseph Glanvill, Plus Ultra, or, The Progress and Advancement of Knowledge since the Days of Aristotle, London: James Collins, Chapter 11, p. 79, How defective the Art of Navigation was in elder Times, when they Sailed by the observation of the Stars, is easie to be imagin’d: For in dark weather, when their Pleiades, Helice, and Cynosura were hidden from them by the intervening Clouds, the Mariner was at a loss for his Guide, and exposed to the casual conduct of the Winds and Tides.”

6. 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.

   “an application for leave (i.e. permission) to intervene”