Online Google Dictionary

billionth 中文解釋 wordnet sense Collocation Usage Collins Definition
  1. position 1,000,000,000 in a countable series of things
  2. the ordinal number of one billion in counting order
  3. one-billionth: one part in a billion equal parts
  4. One billionth is the reciprocal of a billion, which means it has one of two definitions depending on whether the long scale or short scale definition is being used.