zepto-

Zepto- is a combining form used like a prefix meaning “one sextillionth (10-21) .” It is very occasionally used in scientific terms to name units.

Zepto- comes from an alteration of the form hepta-, from Greek heptá, meaning “seven.” The name is a reference to 10-21, which is equivalent to 1000-7. To learn more, read our Words That Use article on hepta-. The z in zepto- was added as part of a reverse alphabetical paradigm for creating numerical combining forms, along with yocto- (10-24); compare with zetta-, meaning “one sextillion,” by reading our Words That Use article on that form.

One example of a technical term that uses the form zepto- is zeptosecond, “one sextillionth (10-21) of a second.”

The zepto- part of the word means “one sextillionth,” and -second here refers to the unit of measure of time that is “the sixtieth part of a minute.” Zeptosecond literally translates to “one sextillionth of a second.”

What are some words that use the combining form zepto-?

• zeptobar
• zeptogram
• zeptometer
• zeptomolar

What are some other forms that zepto- may be commonly confused with?

• septi-
• septo-
• zetta-
• zygo-

Given the meaning of zepto-, what is a zeptometer?