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表示顺序的数词叫序数词。除特殊情况外，序数词一般由相应的基数词加后缀-th构成。
一、序数词如下表所示：
|
第一到第十 |
简写 |
第十一到第十九 |
简写 |
第二十以上 |
简写 |
|
first |
1st |
Eleventh |
11th |
twentieth |
20th |
|
second |
2nd |
Twelfth |
12th |
thirtieth |
30th |
|
third |
3rd |
Thirteenth |
13th |
fortieth |
40th |
|
fourth |
4th |
Fourteenth |
14th |
fiftieth |
50th |
|
fifth |
5th |
Fifteenth |
15th |
sixtieth |
60th |
|
sixth |
6th |
Sixteenth |
16th |
seventieth |
70th |
|
seventh |
7th |
Seventeenth |
17th |
eightieth |
80th |
|
eighth |
8th |
Eighteenth |
18th |
ninetieth |
90th |
|
ninth |
9th |
Nineteenth |
19th |
hundredth |
100th |
|
tenth |
10th |
thousandth |
1000th |
二、序数词的写法
（1） 英语中序数词1st-19th除第一(first), 第二（second）,第三(third)有特殊形式外，其余均由相应的基数词加-th构成。
（2） 表示“第几十”的整十序数词通常是将基数词词尾的y变成ie,再加上后缀-th
Twenty-twentieth forty-fortieth
(3) hundred、thousand、million、billion的序数词均在其后加-th.
(4 ) 基数词“几十几“变成序数词，仅将个位数变成序数词，十位数不变。
sixty-first第六十一 seventy-second第七十二
(5) 序数词可缩写为阿拉伯数字加序数词最后的两个字母
第一first- 1st 第二second-2nd 第三third-3rd
第五fifth-5th 第九十七 ninety-seventh -97th
