The eighth item in a series is the one that you count as number eight.
the eighth prime minister of India.
印度的第八任总理。
eighths
An eighth is one of eight equal parts of something.
The Kuban produces an eighth of Russia's grain, meat, and milk.
库班河流域出产俄罗斯八分之一的谷物、肉类和牛奶。