Billionth (adjective)

Constituting number 1,000,000,000 in a series; occurring in position number 1,000,000,000 in a series.

Origin:

Originated in the late 17th century, from 'billion' + '-th'.

Examples:

1. The billionth digit of pi is 9.
2. The company's billionth customer received a special prize.
3. The space probe reached its billionth kilometer of travel.
4. The scientist made a breakthrough on his billionth attempt.
5. The billionth drop of water in the bucket caused it to overflow.