Google
  Web Word Quests Site   

There are two search terms on this page.
 


zepto- [ZEP toh] (Latin: septo-, seven; a decimal prefix used in the international metric system for measurements).

This prefix is used in the metric [decimal] system as sextillionth [U.S.] or quadrillionth part [U.K.], 10-21 [0.000 000 000 000 000 000 001]. The metric symbol is z.