三等的英文：
third class

参考例句：

I took my seat in a third-class carriage of a deserted train.
我在一列空荡荡的火车的三等车厢找了个座位。

A small, pale child's face could be seen in the gloom of a third-class carriage
在那一列车的一个昏暗的三等车厢里坐着一个身材瘦小，面色苍白的小孩儿。

third是什么意思：
num. 第三，三分之一
adj. 第三的；三分之一的

One third of the population are townsmen and two thirds countrymen.
三分之一的人口是住在城里，三分之二住在乡下。

Passing of the Third Floor Back
四楼尽头的信道

The third coordinate is elevation.
第三项坐标是高程。

Will Spurs be relegated to the third division?
斯珀尔斯队会降为丙级队吗?

Third, have faith in your job.
第三，要对你的工作有信心。

class是什么意思：
n. 班级；阶级；种类
v. 分类；把…分等级
adj. 很好的

It is a step class.
这是踏板操训练班。

The class dismissed.
下课了。

The class teacher sectioned the class for dialogues.
老师把班级分组进行对话练习。

The class teacher dismissed the class on time.
教师按时下课。

A second - class letter is slower than a first - class.
二类信比一类信件慢。