zepto-, abbreviated z (numerical prefix): in the International System of Units the prefix zepto- multiplies the unit to which it is attached by 10-21, which can be rewritten as (10-3)7, the seventh power of one one-thousandth. Zepto- is from the Latin stem sept- “seven,” with the final -o added for uniformity: all of the numerical prefixes in the International System of Units have two syllables and end in a vowel, which in the case of submultiples created in recent times is always an -o. The initial s- of the Latin word was changed to z- to avoid confusion with the prefix sept- that occurs in words like septillion; furthermore, the abbreviation s was already in use for seconds, but z was still available. The prefix zepto- was proposed in 1990 and was officially adopted as part of the International System of Units in 1991. Compare yocto-. [191]

zero, plural zeros or zeroes (cardinal number): a variant of the Arabic word çifr “empty,” translated from the corresponding Hindu word sunya, since the Hindus apparently were the first to develop the concept of zero. When you use a zero as part of a number written in place-value notation, you are keeping a particular place “empty.” The Arabic word took on varying forms in European languages, including zephirum, zefiro, and cipher (q.v.). The modern form zero seems to have appeared in print for the first time in 1491 in De Arithmetica Opusculum, by Philippi Calandri.