To come, appear, or lie between two things: You can't see the lake from there because the house intervenes.
To come or occur between two periods or points of time: A year intervened between the two dynasties.
To occur as an extraneous or unplanned circumstance: He would have his degree by now if his laziness hadn't intervened.
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).
To interfere, usually through force or threat of force, in the affairs of another nation.
Law To enter into a suit as a third party for one's own interests.
[Latin intervenīre : inter-, inter- + venīre, to come; see gwā- in Indo-European roots.] in'ter·ve'nor, in'ter·ven'er n., in'ter·ven'tion (-věn'shən) n., in'ter·ven'tion·al adj.
[in-ter-vee-ner] 
tərˈvi