Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
First found in Dan. 3:6, 4:19, 33, 5:5. It is the rendering of the Chaldee shaah, meaning a "moment," a "look." It is used in the New Testament frequently to denote some determinate season (Mt. 8:13; Lk. 12:39).
With the ancient Hebrews the divisions of the day were "morning, evening, and noon-day" (Ps. 55:17, etc.). The Greeks, following the Babylonians, divided the day into twelve hours. The Jews, during the Captivity, learned also from the Babylonians this method of dividing time. When Judea became subject to the Romans, the Jews adopted the Roman mode of reckoning time. The night was divided into four watches (Lk. 12:38; Mt. 14:25, 13:25). Frequent allusion is also made to hours (Mt. 25:13, 26:40, etc.).
An hour was the twelfth part of the day, reckoning from sunrise to sunset, and consequently it perpetually varied in length.