1. being number one billion in a sequence

1. one of a billion equal parts of something
2. the person or thing that is number one billion in a sequence

Examples

• She was the billionth customer to visit the store.
• The computer can process data in billionths of a second.
• A nanosecond is one billionth of a second.
• The billionth digit of pi has been calculated.
• The measurement was accurate to within a billionth of a meter.
• He became the billionth person to use the app.
• The particle was only a billionth the size of a grain of sand.