##### The Collaborative International Dictionary

**Le Systeme International de Unit'es**

Metric system \Met"ric sys"tem\n. A system of weights and measures originating in France, the use of which is required by law in many countries, and permitted in many others, including the United States; the system is also called by its French name, Le Syst[`e]me International de Unit['e]s (abbreviated SI). The principal unit of length is the meter (see Meter). From this are formed the are, the liter, the stere, the gram, etc. These units, and others derived from them, are divided decimally, and larger units are formed from multiples by 10, 100, 1,000, and 10,000. The successive multiplies are designated by the prefixes, deka- (formerly deca-), hecto-, kilo-, and myria- (seldom used); successive parts by deci-, centi-, and milli-. The prefixes mega- and micro- are used to denote a multiple by one million, and the millionth part, respectively; giga- and nano- denote multiples of one billion (1,000,000,000) and one billionth, respectively. The prefix for one trillion (1012) is tera, and for one trillionth (10-12) is pico; for one quintillion (1015) peta, and for (10-15) (one quintillionth) femto; for (10-18) atto. See the words formed with these prefixes in the Vocabulary. For metric tables, see p. 1682.