intervene (v.) Look up intervene at Dictionary.com
1580s, "intercept" (obsolete), a back-formation from intervention, or else from Latin intervenire "to come between, intervene; interrupt; stand in the way, oppose, hinder," from inter "between" (see inter-) + venire "to come," from a suffixed form of PIE root *gwā- "to come" (see come). Sense of "come between, fall or happen between" (of events) is from c. 1600; that of "interfere, interpose oneself between, act mediatorially" is from 1640s. Related: Intervened; intervener; intervening.