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third class

5.3

Mail sent at a lower price, usually for advertising flyers

noun

Archaic

: correo de tercera clase

The post office no longer offers third class rates, as services have been renamed.

Examples

Sending the newsletter as third class significantly reduced shipping costs for the publisher.
I received a letter sent via third class mail.
Many businesses used third class mail to send out advertising flyers to customers.
The company uses third class for its promotional materials.
Many businesses use third class mail to send out promotional materials at a lower cost.
The company decided to send the newsletter using third class postage to save on expenses.
He received an invitation to the event through third class mail, which took longer to arrive.

Synonyms

third-class mail

vsthird class

Archaic

2.8

Printed items sent by post at a lower cost and slower delivery

is the traditional label for the same reduced-rate printed matter

How Fast

express mail

1 2.8

special delivery

14 3.4

first-class mail

Formal

1 2.2

third class

Archaic

5.3

Surface Forms

third class singular

third classes plural

Morphology

third + class

The sense is compositionally built from 'third' (an ordinal indicating a lower rank) + 'class' (a category), so a learner can infer this refers to a lower/third-tier category of mail (lower priority or reduced rate). This ordinal+class schema is common cross-linguistically and in service/ticketing vocabulary, making the MWE immediately understandable to a B1 learner who knows the constituents.

Etymology

Third class mail was a post office category for printed things like flyers and ads that could be sent cheaply and slowly. The post office put these items in the 'third' group, so third class came to mean mail sent at a lower price and lower priority.