Verb

(en verb)

To occur or take place.

*{{quote-magazine, date=2013-06-28, author=(Joris Luyendijk)

, volume=189, issue=3, page=21, magazine=(The Guardian Weekly) , title= Our banks are out of control , passage=Seeing the British establishment struggle with the financial sector is like watching an alcoholic who still resists the idea that something drastic needs to happen for him to turn his life around.}}

To occur unexpectedly, by chance or with a low probability.

To encounter by chance.

* 1860 , , The Marble Faun , ch. 30:

Unexpectedly, in a nook close by the farmhouse, he happened upon a spot where the vintage had actually commenced.

Verb

(ambitransitive) To come between, or to be between, persons or things.

The Mediterranean intervenes between Europe and Africa.

* De Quincey

self-sown woodlands of birch, alder, etc., intervening the different estates

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.

To interpose; as, to intervene to settle a quarrel; get involved, so as to alter or hinder an action

(legal) 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)