Billennium

Billennium (pl. billennia) is a neologism which is a combination either of "billion" and "millennium", that is a period of a billion years, or a combination of "bi-" and "millennium", that is a second millennium, such as that which ended in the year 2000.

The word "billennium" is used by such writers as Madeleine L'Engle (A Wind in the Door), Stanisław Lem (Imaginary Magnitude) and J. G. Ballard in a collection of short stories under the same name, apparently in reference to a billion years.

See also:

• Unix billennium
• Beretta 92 Billennium

The word "billennium" should not be confused with "biennium", a period of two years.