Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
The period following sunset with which the Jewish day began (Gen. 1:5; Mk. 13:35). The Hebrews reckoned two evenings of each day, as appears from Ex. 16:12, 30:8, 12:6 (marg.); Lev. 23:5 (marg. R.V., "between the two evenings"). The "first evening" was that period when the sun was verging towards setting, and the "second evening" the moment of actual sunset. The word "evenings" in Jer. 5:6 should be "deserts" (marg. R.V.).