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.

Major third (Mus.), an interval of two tones. -- Minor third (Mus.), an interval of a tone and a half.