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