(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.
Origin
1835-45
third-class
[thurd-klas, -klahs] /ˈθɜrdˈklæs, -ˈklɑs/
adjective
1.
of the lowest or poorest class or quality; inferior.
2.
least costly and luxurious:
a third-class coach.
adverb
3.
by third-class mail or passenger accommodations:
to travel third-class.
Origin
1830-40
British Dictionary definitions for third class
third class
noun
1.
the class or grade next in value, quality, etc, to the second
adjective (third-class when prenominal)
2.
of the class or grade next in value, quality, etc, to the second
3.
of or denoting the class of accommodation in a hotel, on a ship, etc, next in quality and price to the second: usually the cheapest
4.
(in the US and Canada) of or relating to a class of mail consisting largely of unsealed printed matter