billionth

Everyday

1. Coming as number one billion in order (1,000,000,000th). tree →
2. One of a billion equal parts of something: 1/1,000,000,000. tree →

In the lessons

In maths, ordinal and fraction words. A nanometre is a billionth of a metre and a nanosecond is a billionth of a second. In news, «the billionth visitor» or «the billionth phone sold».

Examples

• A nanosecond is a billionth of a second. tree →
• The company celebrated its billionth customer. tree →
• The world's billionth person was born in the 1800s. tree →
• Write one billionth as a fraction: 1/1,000,000,000. tree →
• Atoms are smaller than a billionth of a metre across. tree →

Note

Maths: a billion today means 1,000,000,000 (a thousand million) in the UK, USA and elsewhere; an old British meaning was a million million. A billionth = 1 ÷ 1,000,000,000 = 0.000000001.