one-billionth

Meanings

1. 1
   noun

   one of a billion equal parts; the quantity 0.000000001 or 10 to the power of negative nine

   One nanosecond is one-billionth of a second.

2. 2
   adj

   occupying position number one billion in a sequence

   The counter recorded its one-billionth event shortly before midnight.

A compound of one + billionth. Billion came through French billion, originally formed from bi- and million; in modern English it normally denotes one thousand million. The ordinal suffix -th creates billionth, and the prefixed one makes the fractional quantity explicit.

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