first-class

名词 first-class:

1. the highest rank in a classification
   同义词：first class
2. mail that includes letters and postcards and packages sealed against inspection
   同义词：first class, 1st class, first-class mail, 1st-class mail
3. the most expensive accommodations on a ship or train or plane
   同义词：first class

形容词 first-class:

1. of the highest quality
   同义词：excellent, fantabulous

副词 first-class:

1. by first-class conveyance; with first-class accommodations

first-class

adj.（形容词）
Constituting or belonging to the first, highest, or best group in a system of classification:
一流的，甲等的：构成或属于一个分类系统中最先的、最高的或最好一组的：
例句：
a first-class hotel; first-class mail.
一家一流的旅馆；一类邮件

Of the foremost excellence or highest quality; first-rate:
极好的，一流的：最优秀的或质量最高的；最高等级的：
例句：
a first-class mind.
一颗高尚的心

【引伸】
first. class.
adv.（副词）