*2. a. intr. To occur at the same successive instants of time; to keep time with; to go on at the same rate and exactly together; to have coincident periods, as two sets of [[movements]] or [[vibration]]s. | *2. a. intr. To occur at the same successive instants of time; to keep time with; to go on at the same rate and exactly together; to have coincident periods, as two sets of [[movements]] or [[vibration]]s. |