xenno-

From Ancient Greek ἐννέα (ennéa, “nine”), for the ninth order of 10³; with the letter x added for the third term in a series running backwards through the alphabet (after zepto- and yocto-). The final o conforms to the final vowels of the SI series from micro- downwards.

xenno-

1. (informal) Synonym of ronto- (used before an official prefix existed). Symbol: x
   • 1994, IPC Magazines, New Scientist, volume 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.

   • 2002, Greg Egan, Schild's Ladder, Gollancz, published 2008, page 184:

     'Now we're talking xennobiology!' [...] a complex organism based on similar processes to the primitive ones they'd seen probably would be about a xennometre in size.

   • 2004 November, Seth Lloyd, Y. Jack Ng, “Black Hole Computers”, in Scientific American, page 56:

     From Nanotech to Xennotech [...] A one-kilogram hole has a radius of about 10^-27 meter.

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

• xenna-

• xenon, Noxen