the best, finest, or highest class, grade, or rank.
2.
the most expensive and most luxurious class of accommodation on trains, ships, airplanes, etc.
3.
(in the U.S. Postal Service) the class of mail consisting of letters, postal cards, or the like, together with all mailable matter sealed against inspection.
4.
British University. the group receiving the highest distinction in an honors course.
Origin
1740-50
first-class
[furst-klas, -klahs] /ˈfɜrstˈklæs, -ˈklɑs/
adjective
1.
of the highest or best class or quality:
a first-class movie.
2.
best-equipped and most expensive:
a first-class railroad car.
3.
given or entitled to preferred treatment, handling, etc.:
first-class mail.
adverb
4.
by first-class conveyance:
to travel first-class.
Origin
1780-90
British Dictionary definitions for first class
first class
noun
1.
the class or grade of the best or highest value, quality, etc
adjective (first-class when prenominal)
2.
of the best or highest class or grade: a first-class citizen
3.
excellent; first-rate
4.
of or denoting the most comfortable and expensive class of accommodation in a hotel, aircraft, train, etc
5.
(in Britain) of or relating to mail that is processed most quickly
(in the US and Canada) of or relating to mail that consists mainly of written letters, cards, etc