1. the class, grade, or rank immediately below the second.
2. the least costly class of accommodations on trains, in hotels, etc. Cf. tourist class. 3. (in the U.S. Postal Service) the class of mail consisting of merchandise weighing up to 16 ounces, and written or printed material, as books, manuscripts, or circulars, not sealed against postal inspection.
4. the lowest of three honors degrees conferred by a British university.
Pronunciation: (thûrd'klas', -kläs'),[key] —adj. 1. of the lowest or poorest class or quality; inferior.
2. least costly and luxurious: a third-class coach.
—adv. by third-class mail or passenger accommodations: to travel third-class.