Third a.
 1. Next after the second; coming after two others; -- the ordinal of three; as, the third hour in the day. “The third night.”
 2. Constituting or being one of three equal parts into which anything is divided; as, the third part of a day.
 Third estate. (a) In England, the commons, or the commonalty, who are represented in Parliament by the House of Commons. (b) In France, the tiers état. See Tiers état. Third order R. C. Ch., an order attached to a monastic order, and comprising men and women devoted to a rule of pious living, called the third rule, by a simple vow if they remain seculars, and by more solemn vows if they become regulars. See Tertiary, n., 1.
 Third person Gram., the person spoken of. See Person, n., 7.
 Third sound. Mus. See Third, n., 3.