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From Ancient Greek ἐννέα (ennéa, nine), for the ninth order of 103, and the letter x, as the third term in a series running backwards through the alphabet (after zetta- and yotta-). The final a conforms to the final vowel of the SI series from mega- upwards.




  1. (neologism) In metric systems of units, multiplying the unit to which it is attached by 1027; octillion-. Symbol: X
    • 1994, IPC Magazines, New Scientist Vol. 144, page 81:
      The SI prefixes above are not the only extreme ones. Others such as xenno (x) (10-27) and xenna (X) (1027), or vendeko (v) (10-33) and vendeka (V) (1033) exist, and can help simplify the expression of extreme numbers.
    • 1997, Council of Scientific & Industrial Research, Science Reporter Vol. 34, page 23:
      If we try to calculate the mass of earth it comes to 6 xennagrams which is nothing but 6x1024 kilograms or 6x1027 gms.
    • 2015, Claude Phipps, No Wonder You Wonder!: Great Inventions and Scientific Mysteries, Springer, page 62:
      But that's nothing: our universe is about 0.8 Xm (Xennametres, billions of billions of billions of metres) in diameter.
    • For more examples of usage of this term, see Citations:xenna-.

Usage notes[edit]

Not a standard prefix in the metric International System of Units.

Derived terms[edit]