billionth /ˈbɪljənθ/ (billionths)

• 1.  

  ORD（序数词） The billionth item in a series is the one you count as number one billion. 第10亿个

  例：

  I have to go after Steve Mercer, she thought for probably the billionth time.

  我一定要去找史蒂夫·默瑟，这大概是她第十亿次这样想了。

• 2.  

  FRACTION（分数词） A billionth is one of a billion equal parts of something. 十亿分之一

  例：

  ...a billionth of a second.

  ...十亿分之一秒。