first class

adverb

Definition

› If you travel first class in a train, aircraft, etc., you use the best and most expensive type of service: She always travels first class. › UK If you send something first class, you use the most expensive and fastest type of post: How much more would it cost to send it first class?

(Definition of first class adverb from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)