noun [in singular]
a group of people or things considered together as third best. British a university degree or examination result in the third-highest classification. US a cheap class of mail for advertising and other printed material that weighs less than 16 ounces and is unsealed.
chiefly historical the cheapest and least comfortable accommodations in a train or ship.
adjective & adverb
of the third-best quality or of lower status: [as adjective]:many indigenous groups are still viewed as third-class citizens [as adjective] British of or relating to the third-highest division in a university examination:he left university with a third-class degree US of or relating to a cheap class of mail including advertising and other printed material weighing less than 16 ounces: [as adjective]:third-class mail
chiefly historical of or relating to the cheapest and least comfortable accommodations in a train or ship: [as adjective]:a suffocating third-class compartment [as adverb]:I traveled third class across Europe