first class

Từ điển Oxford Advanced Learner 8th

ˌfirst ˈclass [first class] noun, adverb BrE NAmE
noun uncountable
1. the best and most expensive seats or accommodation on a train, plane or ship
•There is more room in first class.
2. (in Britain) the class of mail that is delivered most quickly
•First class costs more.
3. (in the US) the class of mail that is used for letters
4. the highest standard of degree given by a British university
 
adverb
1. using the best and most expensive seats or accommodation in a train, plane or ship
•to travel first class
2. (in Britain) by the quickest form of mail
•I sent the package first class on Monday.
3. (in the US) by the class of mail that is used for letters