1. 第一千：thousands 数千 | thousandth 第一千 | Thrace 色雷斯

2. 千分比：Thickness 厚度 t | Thousandth 千分比 ‰ | Ton 公吨 T

3. 千分之一的：path 小道;小径 | thousandth 千分之一的 | wavelength 波长

4. 第一千,千分之一：thorough walk-around inspection;围绕机器的全面检查 | thousandth;第一千,千分之一 | thrd;螺纹

1. 第一千
    The thousandth item in a series is the one that you count as number one thousand.

    e.g. The magazine has just published its six thousandth edition.
           这本杂志刚刚出版了第 6,000 期。

2. 千分之一
    A thousandth is one of a thousand equal parts of something.

    e.g. ...a dust particle weighing only a thousandth of a gram.
           重量仅有千分之一克的灰尘微粒

1. one part in a thousand equal parts

    Synonym: one-thousandth

2. position 1,000 in a countable series of things

1. the ordinal number of one thousand in counting order

    Synonym: 1000th