名詞 first-class:

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

形容詞 first-class:

1. of the highest quality
   同義詞：excellent, fantabulous

副詞 first-class:

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

first-class

adj.（形容詞）
Constituting or belonging to the first, highest, or best group in a system of classification:
一流的，甲等的：構(gòu)成或?qū)儆谝粋€分類系統(tǒng)中最先的、最高的或最好一組的：
例句：
a first-class hotel; first-class mail.
一家一流的旅館；一類郵件

Of the foremost excellence or highest quality; first-rate:
極好的，一流的：最優(yōu)秀的或質(zhì)量最高的；最高等級的：
例句：
a first-class mind.
一顆高尚的心

【引伸】
first. class.
adv.（副詞）