billionth

adj

1. (not-comparable)The ordinal form of the number one billion.

noun

1. The person or thing in the billionth position.
2. One of a billion equal parts of a whole.

   “That is an extraordinary achievement for a spiky ball of genetic material coated in fatty chemicals called lipids, and which measures 80 billionths of a metre in diameter. Humanity has been brought low by a very humble assailant.”