Trilliard

Trilliard is a large-number term used in the long scale system of naming numbers. It designates 10^21, i.e., 1 followed by 21 zeros. In the long scale, the sequence around this value runs: million (10^6), milliard (10^9), billion (10^12), billiard (10^15), trillion (10^18), trilliard (10^21), quadrillion (10^24).

Usage and regional variations: The term is standard in some continental European languages, for example French and German, where a trilliard or Trilliarde designates 10^21. In English, the term is largely obsolete and rarely used outside historical discussion or translations from long-scale languages. For clarity, many writers instead use scientific notation (1×10^21) or explicitly state the scale being used.

Origins and context: The long scale originated in early modern Europe and assigns a new -illion name to each threefold jump after a million. The term trilliard forms part of that pattern and sits between trillion (10^18) and quadrillion (10^24). In modern practice, English has largely abandoned the long scale in favor of the short scale, which names 10^21 as sextillion. As a result, trilliard is encountered mainly in historical texts or translations.

Related terms: Milliard (10^9) is the corresponding lower unit, and billiard (10^15) and trillion (10^18) are adjacent long-scale terms.

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