where the votes of a deliberative assembly or legislative body are equally divided on any question or motion, it is the privilege of the presiding offl-cer to cast one vote (lf otherwise he would not he entitled to any vote) on either side, or to cast one additional vote, if he has al-ready voted as a member of the body. This is called the “casting vote.”
Source: Black's Law Dictionary 2nd Ed (1910)
